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Satoru Adachi
Faculty of Engineering　Applied Physics　Optical Science and Technology
Professor
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Last Updated :2024/05/09

Researcher Profile and Settings

Affiliation

  • Faculty of Engineering　Applied Physics　Optical Science and Technology

Job Title

  • Professor

Degree

  • Doctor of Engineering（Osaka University）
  • 1988 March ME (Osaka University)（Osaka University）

J-Global ID

Research Interests

  • Spintronics   Quantum Electronics   Laser Spectroscopy   Solid-State Photo-Physics   

Research Areas

  • Natural sciences / Semiconductors, optical and atomic physics
  • Nanotechnology/Materials / Nanostructure physics
  • Nanotechnology/Materials / Applied materials

Educational Organization

Academic & Professional Experience

  • 2010/04 - Today Hokkaido University Faculty of Engineering Division of Applied Physics Professor
  • 2000/04 - 2010/03 Hokkaido University Faculty of Engineering Division of Applied Physics Associate Professor
  • 1991 - 2000 Himeji Institute of Technology Department of Material Science Assistant Professor

Education

  •        - 1991  Osaka University
  •        - 1991  Osaka University  Graduate School, Division of Engineering  Division of electrical Engineering
  •        - 1988  Osaka University
  •        - 1988  Osaka University  Graduate School, Division of Engineering  Division of Electrical Engineering
  •        - 1986  Osaka University  School of Engineering
  •        - 1986  Osaka University  Faculty of Engineering  Division of Electric Engineering

Association Memberships

  • 応用物理学会   The Japan Society of Applied Physics   

Research Activities

Published Papers

  • S. Yamamoto, R. Kaji, S. Adachi
    Physical Review B 108 (5) 054422/1 - 054422/11 2469-9950 2023/08/16 [Refereed]
  • Shoichiro Yasui, Masaya Hiraishi, Atsushi Ishizawa, Hiroo Omi, Tomohiro Inaba, Xuejun Xu, Reina Kaji, Satoru Adachi, Takehiko Tawara
    Optics Continuum 1 (9) 1896 - 1908 2022/08/10 [Refereed]
  • S. Yasui, M. Hiraishi, A. Ishizawa, H. Omi, R. Kaji, S. Adachi, T. Tawara
    Optics Express 29 (17) 27137 - 27148 2021/08/16 [Refereed]
  • S. Yamamoto, R. Kaji, H. Sasakura, S. Adachi
    Japanese Journal of Applied Physics 60 (SB) SBBH07/1 - SBBH07/4 0021-4922 2021/05/01 [Refereed]
     
    Abstract Hyperfine interaction in a quantum dot produces a spin-coupled system between an injected electron and a few tens of thousands of nuclei in the electron wavefunction. We report here that the double bistable phenomenon of nuclear spin polarization (NSP) can be observed by sweeping three control parameters. All the observations indicate that the NSP has three stable branches under a longitudinal magnetic field, whereas the number of the stable branches of NSP has been believed to be two at most. The incorporation of the electron spin relaxation due to the nuclear spin fluctuation enables reproduction of the observed features of the NSP and the electron spin polarization.
  • S. Yamamoto, R. Kaji, H. Sasakura, S. Adachi
    Physical Review B 101 (24) 245424/1 - 245424/8 2469-9950 2020/06/17 [Refereed]
  • Sota Yamamoto, Takuya Arakawa, Ryosuke Matsusaki, Reina Kaji, Satoru Adachi
    physica status solidi (b) 257 (2) 1900381/1 - 1900381/5 0370-1972 2020/02 [Refereed]
  • Masaya Hiraishi, Mark IJspeert, Takehiko Tawara, Satoru Adachi, Reina Kaji, Hiroo Omi, Hideki Gotoh
    Optics Letters 44 (20) 4933 - 4936 0146-9592 2019/10/15 [Refereed]
  • S. Yamamoto, R. Matsusaki, R. Kaji, S. Adachi
    Journal of Physics: Conference Series 1220 (1) 012047/1 - 012047/4 1742-6588 2019/05 [Refereed]
     
    Abstract We studied the formation mechanism of in-plane nuclear field by anomalous Hanle effect measurements in single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dots and InAs/GaAs quantum rings. The observed anomalous Hanle curves indicated quite large width and hysteretic behavior to the externally applied magnetic field. These anomalies appears in both materials whose electron g factors have opposite sign each other, and cannot be reproduced by a traditional spin dynamics model. In this study, we show that a proposed spin dynamics model can explain the formation of a large in-plane nuclear field regardless of the sign of electron g factor. The model is based on the dynamic nuclear spin polarization mechanism including the effects of nuclear quadrupole interaction.
  • Reina Kaji, Sota Yamamoto, Ryosuke Matsusaki, Satoru Adachi
    Japanese Journal of Applied Physics 58 (SB) SBBH10/1 - SBBH10/6 0021-4922 2019/04/01 [Refereed]
  • Reina Kaji, Ryosuke Matsusaki, Sota Yamamoto, Satoru Adachi
    Japanese Journal of Applied Physics 58 (SB) SBBH05/1 - SBBH05/5 0021-4922 2019/04/01 [Refereed]
  • Hiraishi Masaya, Mark IJspeert, Tawara Takehiko, Adachi Satoru, Omi Hiroo, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2019.1 2828 - 2828 2019/02/25
  • Ryosuke Matsusaki, Reina Kaji, Sota Yamamoto, Hirotaka Sasakura, Satoru Adachi
    Applied Physics Express 11 (8) 085201/1 - 085201/5 1882-0778 2018/08/01 [Refereed]
  • Satoru Adachi, Yoshihiro Kawakami, Reina Kaji, Takehiko Tawara, Hiroo Omi
    Applied Sciences 8 (6) 874/1 - 874/13 2076-3417 2018/05/25 [Refereed]
  • S. Yamamoto, R. Matsusaki, R. Kaji, S. Adachi
    Physical Review B 97 (7) 075309/1 - 075309/8 2469-9950 2018/02/26 [Refereed]
  • IJspeert Mark, Mariani Giacomo, Tawara Takehiko, Shimizu Kaoru, Omi Hiroo, Adachi Satoru, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2017.2 3008 - 3008 2017/08/25
  • Takehiko Tawara, Giacomo Mariani, Kaoru Shimizu, Hiroo Omi, Satoru Adachi, Hideki Gotoh
    Applied Physics Express Institute of Physics 10 (4) 042801/1 - 042801/4 1882-0778 2017/04/01 [Refereed]
     
    We investigated spectral-hole narrowing in optical transitions between hyperfine sublevels in isotopically purified erbium ions (167Er3+). The homogeneous broadening Γhof the optical transition was measured in purified and non-purified Er3+-doped crystals via spectral-hole burning. The measured Γhin the purified 167Er3+exhibited a significant reduction of the hole width because the fluctuation of the local magnetic field induced by the electron spins of the surrounding Er3+ions was eliminated. Because the narrowing of the Γhis equivalent to the prolongation of the coherence time, the isotopic purification is effective for the coherent manipulation of quantum states.
  • Takehiko Tawara, Yoshihiro Kawakami, Hiroo Omi, Reina Kaji, Satoru Adachi, Hideki Gotoh
    OPTICAL MATERIALS EXPRESS 7 (3) 1097 - 1104 2159-3930 2017/03 [Refereed][Not invited]
     
    We have optically investigated the characteristics of concentration quenching in epitaxial (ErxSc1-x)(2)O-3 layers at the liquid helium temperature as a function of the Er composition (x = 1.000-0.012). Concentration quenching with increasing Er composition was observed at the lowest optical transition energy, although emission lifetimes of 2 ms were maintained from x = 0.012 to 0.270. An analysis of the excitation power dependence of the emission intensity at the lowest and up-converted transition energies revealed that the concentration quenching in high-quality epitaxial (ErxSc1-x)(2)O-3 films mainly originates from the population escaping to the up-conversion states with a high transfer rate, not the population transfer among Er3+ sites to non-radiative centers. (C) 2017 Optical Society of America
  • R. Kaji, T. Tominaga, Y.-N. Wu, M.-F. Wu, S.-J. Cheng, S. Adachi
    physica status solidi (b) 254 (2) 1600486 - 1600486 0370-1972 2017/02 [Refereed]
  • L.-P. Yan, T. Takamure, R. Kaji, G. Karczewski, S. Takeyama, S. Adachi
    physica status solidi (b) 254 (2) 1600449/1 - 1600449/6 0370-1972 2017/02 [Refereed]
  • Takehiko Tawara, Giacomo Mariani, Kaoru Shimizu, Hiroo Omi, Satoru Adachi, Hideki Gotoh
    Conference on Lasers and Electro-Optics (CLEO:2017) 2160-9020 2017 [Refereed][Not invited]
     
    We report effect of isotope separation on the homogeneous linewidth in Er3+-doped Y2SiO5 measured by using spectral hole burning. Isotope Er-167(3+) provides a drastic reduction of the spectral hole width by strongly suppressing instantaneous spectral diffusion.
  • Tawara Takehiko, Mariani Giacomo, Shimizu Kaoru, Omi Hiroo, Adachi Satoru, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2016.2 2817 - 2817 2016/09/01
  • Hamada Yuki, Tawara Takehiko, Apache Satoru, Llenas Aleix, Omi Hiroo, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2016.1 3078 - 3078 2016/03/03
  • R. Kaji, T. Tominaga, Y. -N. Wu, M. -F. Wu, S. -J. Cheng, S. Adachi
    The 43rd International Symposium on Compound Semiconductors (ISCS) 2016 [Refereed][Not invited]
     
    We investigated the electron and hole g-factors in individual InAs/GaAs quantum rings (QRs). From the magneto-photoluminescence measurements under a transverse magnetic field, we evaluated the in-plane g-factors of electron and hole spins by rotating the sample systematically around the crystal growth axis. The experimental results indicate that the in-plane and the out-of-plane anisotropies in hole g-factor are larger than those of electron g-factor, and the value of the hole in-plane g-factor varies largely from QR to QR while the electron g-factor is almost a constant value. From the model calculation considering the effects of shape anisotropies and uniaxial stress, we examined the correlation between the in-plane g-factors and the degree of valence band mixing. Further, the experimentally obtained trend in g-factors was in agreement qualitatively with theoretical consideration.
  • Takehiko Tawara, Hiroo Omi, Thomas McManus, Aleix Llenas, Eiichi Kuramochi, Satoru Adachi, Hideki Gotoh
    The 43rd International Symposium on Compound Semiconductors (ISCS) 2016 [Refereed][Not invited]
  • L. -P. Yan, R. Kaji, S. Adachi
    The 43rd International Symposium on Compound Semiconductors (ISCS) 2016 [Refereed][Not invited]
     
    We have studied the spin dynamics of the resident electron spin polarization (RESP) based on the initial phase shift of the Larmor precessions in a CdTe single quantum well by using a time-resolved Kerr rotation technique. The generation dynamics of RESP involve the formation and transformation of the associated optically excited states and are complicated particularly in the early time region. A careful analysis of the phase shift gives a deep understanding of the generation processes. In the experiments in the excitation energy range between the negative trion and neutral exciton resonances, the anomalous negative phase shift was observed, and the mechanism associated especially with a quick hole spin-flip and transformation to trions from excitons are discussed through the dependences on excitation energy, excitation power, and magnetic field strength.
  • S Adachi, Y Kawakami, R Kaji, T Tawara, H Omi
    Journal of Physics: Conference Series 647 012031 - 012031 1742-6588 2015/10/13 [Refereed]
  • Li-Ping Yan, Masahiro Kurosawa, Wei-Ting Hsu, Wen-Hao Chang, Satoru Adachi
    Japanese Journal of Applied Physics Institute of Physics 54 (3) 033003 - 033003 0021-4922 2015/03/01 [Refereed]
     
    Longitudinal and in-plane electron g-factors, and a nuclear spin polarization (NSP) have been evaluated precisely in a CdTe/Cd0.85Mg0.15Te single quantum well by using the time-resolved Kerr rotation and double lock-in detection techniques. Resident electron spin polarization (RESP) was formed via the negative trion formation and recombination, and RESP gave rise to NSP in an oblique magnetic field configuration. We observed the effective nuclear field of a few mT which was weak compared with that in III–V semiconductor nanostructures as expected, but the nuclear field can be converted to the maximal NSP of 12% in Faraday geometry.
  • Kawakami Yoshihiro, Tawara Takehiko, Omi Hiroo, Kaji Reina, Adachi Satoru
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2015.1 2983 - 2983 2015/02/26
  • R. Kaji, T. Tominaga, Y. -N. Wu, S. -J. Cheng, S. Adachi
    19TH INTERNATIONAL CONFERENCE ON ELECTRON DYNAMICS IN SEMICONDUCTORS, OPTOELECTRONICS AND NANOSTRUCTURES (EDISON' 19) 647 012011/1 - 4 1742-6588 2015 [Refereed][Not invited]
     
    The electron and hole in-plane g-factors were studied in individual InAs/GaAs quantum rings (QRs). From the magneto-photoluminescence measurements under a transverse magnetic field, we evaluated the in-plane g-factors of electron and hole spins by rotating the sample systematically along the crystal growth axis. The experimental results indicate that the in-plane and the out-of-plane anisotropies in hole g-factor are larger than those of electron g-factor, and the value of the hole in-plane g-factor varies largely from QR to QR while the electron g-factor is almost a constant value. From the model calculation considering the effects of shape anisotropies and uniaxial stress, we examined the correlation between the in-plane g-factors and the degree of valence band mixing. Further, the experimentally obtained trend in g-factors was in agreement qualitatively with theoretical consideration.
  • T. Tawara, T. McManus, Y. Kawakami, H. Omi, A. Najar, R. Kaji, S. Adachi, H. Gotoh
    2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2015 [Refereed][Not invited]
     
    Visible up-conversion luminescence induced by 1535-nm excitation in (ErSc)(2)O-3 epitaxial layers are observed. We investigate fast up-conversion rate and propose its suppression structure by photonic band-gap for realizing higher optical gain devices on Si wafers.
  • L.-P. Yan, M. Kurosawa, R. Kaji, G. Karczewski, S. Takeyama, S. Adachi
    Physical Review B American Physical Society 90 (20) 1098-0121 2014/11/19 [Refereed]
     
    Initial phase shift in a precessional motion of resident electron-spin polarization is studied in a CdTe/Cd0.85Mg0.15Te single quantum well using a time-resolved Kerr rotation technique. The generation dynamics of resident electron-spin polarization involve the formation and transformation of the associated optically excited states and are complicated particularly in the early time region. A careful analysis of the phase shift gives a deep understanding of the generation processes. In the experiments, the negative phase shift of the resident electron-spin polarization is observed, and the mechanism associated especially with a quick hole spin flip in negative trions is studied through the dependences on excitation power and magnetic field strength.
  • Kawakami Yoshihiro, Kaji Reina, Adachi Satoru, Tawara Takehiko, Omi Hiroo
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2014.2 2956 - 2956 2014/09/01
  • Omi Hiroo, Tawara Takehiko, Kaji Reina, Adachi Satoru, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2014.2 2959 - 2959 2014/09/01
  • Tawara Takehiko, Omi Hiroo, Najar Adel, Kaji Reina, Adachi Satoru, Gotoh Hideki
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2014.2 2955 - 2955 2014/09/01
  • Reina Kaji, Takahito Hozumi, Yuta Hachiyama, Takuma Tomii, Hirotaka Sasakura, Masafumi Jo, Satoru Adachi
    Applied Physics Express Institute of Physics 7 (6) 065002 - 065002 1882-0778 2014/06/01 [Refereed]
  • Li Ping Yan, Reina Kaji, Satoru Adachi
    Advanced Materials Research 936 534 - 539 1662-8985 2014/06 [Refereed]
     
    Effective magnetic field of nuclear spin polarization (NSP) under circularly polarized pumps excitation and the dephasing time of resident electron spin polarization under pump and control excitation has been detected in a single CdTe quantum well (QW) by a time-resolved Kerr rotation (TRKR) technique. We deduced that the experimental method is verified with the effect, to a certain extent, through confirming the external magnetic field results. In addition, the nuclear field is revealed to be increased with the increasing electron spin component due to the enhanced electron-nuclear hyperfine interaction. Significant nuclear field is observed as 1.85 mT with the applied magnetic field tilted by about 15 degree. What is more, we found the spin dephasing time (SDT) has little relation with the created NSP field, but it decreases largely with the increasing spin polarization magnitude under pump excitation and the spin vector dispersions induced by control pulses.
  • Omi Hiroo, Tawara Takehiko, Kaji Reina, Hozumi Takahito, Adachi Satoru, Goto Hideki, Sougawa Tetuomi
    JSAP Annual Meetings Extended Abstracts 公益社団法人 応用物理学会 2014.1 3089 - 3089 2014/03/03
  • T. Tawara, H. Omi, A. Najar, R. Kaji, S. Adachi, H. Gotoh
    2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2014 [Refereed][Not invited]
     
    Toward quantum information applications, we control the interactions between Er ions by alloying epitaxial Er2O3 with scandium and suppress energy transfer and inhomogeneous broadening of Stark levels in the intra-4f band of Er ions.
  • 俵 毅彦, 尾身 博雄, 穂積 貴人, 鍜治 怜奈, 足立 智, 後藤 秀樹, 寒川 哲臣
    応用物理学会学術講演会講演予稿集 公益社団法人 応用物理学会 2013.2 3700 - 3700 2013/08/31
  • 尾身 博雄, 俵 毅彦, 鍛冶 玲奈, 穂積 貴人, 足立 智, 後藤 秀樹, 寒川 哲臣
    応用物理学会学術講演会講演予稿集 公益社団法人 応用物理学会 2013.2 3842 - 3842 2013/08/31
  • 川上 欣洋, 穂積 貴人, 鍜治 怜奈, 足立 智, 俵 毅彦, 尾身 博雄
    応用物理学会学術講演会講演予稿集 公益社団法人 応用物理学会 2013.2 3701 - 3701 2013/08/31
  • Yasunori Toda, Kyohhei Shigematsu, Akira Hasegawa, Satoru Adachi
    Japanese Journal of Applied Physics The Japan Society of Applied Physics 52 (8S) 08JL03 - 08JL03 0021-4922 2013/08/01 [Refereed]
     
    We report on the four-wave mixing (FWM) spectroscopy of excitons in tensile-strained GaN films. Three excitonic resonances (A-, B-, and C-excitons) were clearly observed with energy separations of \Delta_{\text{AB } }\sim 4.7 meV and \Delta_{\text{BC } }\sim 14.5 meV. Owing to tensile strain, these values are much smaller than those of free-standing GaN, allowing the simultaneous excitations of A--B and B--C excitons pairs. The time evolutions of the FWM in different polarization configurations resolved the differences in the simultaneous excitonic transitions; the excitation of A--B excitons showed an oscillation with a critical \pi-phase shift in the orthogonal polarization configuration as expected in the quantum beat, and the oscillation of B--C excitons pair is independent of the polarization configuration, indicating polarization interference. The polarization-dependent FWM spectra of A--B excitons revealed peaks associated with biexciton transitions with binding energies of E_{\text{AA } } = 4.6 meV, E_{\text{AB } } = 2.1 meV, and E_{\text{BB } } = 1.7 meV.
  • T. Tawara, H. Omi, T. Hozumi, R. Kaji, S. Adachi, H. Gotoh, T. Sogawa
    Applied Physics Letters 102 (24) 241918 - 241918 0003-6951 2013/06/17 [Refereed]
  • R. Kaji, S. Ohno, T. Hozumi, S. Adachi
    JOURNAL OF APPLIED PHYSICS 113 (20) 203511/1 - 6 0021-8979 2013/05 [Refereed][Not invited]
     
    The effects of valence band mixing on the hole spin coherence in self-assembled InAlAs quantum dots are investigated. The valence band mixing induces not only optical anisotropy in the quantum dot emissions but also heavy hole spin dephasing via the hyperfine interaction with the lattice nuclei. We evaluated the degree of valence band mixing for a number of In0.75Al0.25As/Al0.3Ga0.7As quantum dots from experiments. The magnitude of valence band mixing does not show a clear dependence on the photoluminescence energy, and it is less than 0.25 in our sample. Although the direct measurement with experimental methods has not been carried out at this stage, the effect of valence band mixing on the hole spin coherence is discussed in detail by the calculations. (C) 2013 AIP Publishing LLC.
  • Xiangmeng Lu, Masataka Koyama, Yoshiharu Izumi, Yoshiaki Nakata, Satoru Adachi, Shunichi Muto
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (2) 025602/1 - 4 0021-4922 2013/02 [Refereed][Not invited]
     
    We studied the size distribution and scaling behavior of self-assembled InAlAs/AlGaAs quantum dots (QDs) grown on GaAs in the Stranski-Krastanow (SK) mode by molecular beam epitaxy (MBE) at 480 and 510 degrees C as a function of InAlAs coverage. A scaling function of the volume was found for the first time in ternary alloy QDs. The function was similar to that of InAs/GaAs QDs, which agreed with the scaling function for a two-dimensional submonolayer homoepitaxy simulation with a critical island size of i = 1. However, a characteristic of i = 0 was also found as a tail in a large volume. (C) 2013 The Japan Society of Applied Physics
  • T. Tawara, T. Hozumi, H. Omi, R. Kaji, S. Adachi, H. Gotoh, T. Sogawa
    2013 IEEE Photonics Conference, IPC 2013 149 - 150 2013 [Refereed][Not invited]
     
    Time constants of a resonant energy transfer between Er ions in epitaxial Er2O3 grown on Si(111) are investigated for the coherent manipulation of populations and experimentally estimated to be several microseconds by resonant excitation photoluminescence. © 2013 IEEE.
  • Ayako Takagi, Atsushi Nakamura, Akira Yoshikaie, So-ichiro Yoshioka, Satoru Adachi, Shigefusa F. Chichibu, Takayuki Sota
    JOURNAL OF PHYSICS-CONDENSED MATTER 24 (41) 415801/1 - 8 0953-8984 2012/10 [Refereed][Not invited]
     
    Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Gamma(1) and Gamma(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k perpendicular to a and E parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Gamma(1) transverse mode and two Gamma(5) longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.
  • K. Hazu, S. F. Chichibu, S. Adachi, T. Sota
    JOURNAL OF APPLIED PHYSICS 111 (9) 093522/1 - 6 0021-8979 2012/05 [Refereed][Not invited]
     
    Spectroscopic and temporal four-wave-mixing (FWM) measurements are carried out on a strain-free bulk ZnO single crystal, in order to clarify the valence-band-ordering. Under the collinearly polarized lights with the electric-field component parallel to the c-axis, which can excite dipole-allowed Gamma(1)-excitons, the FWM signal appears only in the energies corresponding to the B-exciton. Under the cross-linear polarization configuration exciting both Gamma(5)- and Gamma(1)-excitons, the FWM signal arising from the two-photon-coherence is absent in the energies corresponding to A-exciton. Both the results indicate that Gamma(1)-exciton state belongs exclusively to B-exciton, meaning that the valence-band ordering is Gamma(9) - Gamma(7) - Gamma(7) in order of decreasing electron energy for the present strain-free ZnO single crystal. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711103]
  • S. Adachi, R. Kaji, S. Furukawa, Y. Yokoyama, S. Muto
    JOURNAL OF APPLIED PHYSICS 111 (10) 103531/1 - 6 0021-8979 2012/05 [Refereed][Not invited]
     
    Nuclear spin diffusion in single self-assembled InAlAs quantum dots was studied by using erase-pump-probe technique. As a measure of nuclear spin polarization, transients of the Overhauser shift (OHS) of positive trion were probed in the respective pulse region. The achieved stable OHS was relaxed with a long depolarization time as long as a few tens of seconds and a diffusion constant of similar to 5 x 10(-15) cm(2)/s was estimated. The slow transfer of the spin energy is considered to be due to the dipole-dipole interaction of the nuclei. In addition, through the magnetic field dependence of OHS, the stability of the nuclear spin polarization was briefly discussed, and the saturated maximum values of OHS were investigated experimentally. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4721902]
  • R. Kaji, S. Adachi, H. Sasakura, S. Muto
    PHYSICAL REVIEW B 85 (15) 155315/1 - 6 1098-0121 2012/04 [Refereed][Not invited]
     
    The spin interaction between an electron and nuclei was investigated optically in a single self-assembled InAlAs quantum dot (QD). In spin dynamics at the initial stage, the fluctuation of nuclear field and the resulting electron spin relaxation time play a crucial role. We examined a positively charged exciton in a QD to evaluate the key physical quantities directly via the temporal evolution measurements of the Overhauser shift and the degree of circular polarization. In addition, the validity of our used spin dynamics model was discussed in the context of the experimentally obtained key parameters.
  • X. M. Lu, Y. Izumi, M. Koyama, Y. Nakata, S. Adachi, S. Muto
    JOURNAL OF CRYSTAL GROWTH 322 (1) 6 - 9 0022-0248 2011/05 [Refereed][Not invited]
     
    The effects of growth conditions on the size and density of self-assembled InAlAs/AlGaAs quantum dots (QDs) grown on GaAs by molecular beam epitaxy (MBE) were studied with an emphasis on their use for single QD spectroscopy. The effects of substrate temperature and growth rate on the density and size were found to be quite similar to those of InAs QDs on GaAs. The effect of coverage, however, was different. Although the density was relatively high as compared to that of InAs QDs, it was reduced to 1 x 10(10) cm(-2) under an optimized condition. This density is compatible with single QD spectroscopy with the help of a certain nanofabrication technique for areal restriction. (C) 2011 Elsevier B.V. All rights reserved.
  • Sou Ryuzaki, Toshihiro Kai, Yasunori Toda, Satoru Adachi, Jun Onoe
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 44 (14) 145103/1-145103/1 - 4 0022-3727 2011/04 [Refereed][Not invited]
     
    We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C-60/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons.
  • S. Ohno, S. Adachi, R. Kaji, S. Muto, H. Sasakura
    APPLIED PHYSICS LETTERS 98 (16) 161912/1-161912/1 - 3 0003-6951 2011/04 [Refereed][Not invited]
     
    We have investigated the optical anisotropy in individual self-assembled quantum dots. The linear polarization analysis of the positive trion photoluminescence reveals the effect of the strain-induced valence band mixing since the positive trion has the spin-paired holes and therefore exchange interaction has no influence. Meanwhile, the neutral exciton indicates the complex polarization states due to both the in-plain asymmetries of the dot shape and the strain distributions. The experimental and theoretical polarization analysis has been performed for tens of InAlAs quantum dots and the correlation between the important parameters was investigated. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3583453]
  • R. Kaji, S. Adachi, S. Muto
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 1 8 (1) 30 - 33 1862-6351 2011 [Refereed][Not invited]
     
    Polarization properties of the exciton emissions from single InAlAs/AlGaAs quantum dots were investigated by using Hanle-like measurement. The in-plane exchange field drives the exciton spin precession even under zero external magnetic field and the polarization of emissions can be converted from circular to linear and vice versa. Longitudinal applied magnetic field increases the conversion ratio up to the theoretical limit similar to 50%, where the field strength is comparable to the exchange field. Finally, the effect of valence band mixing on the polarization conversion was discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • K. Tomoda, S. Adachi, S. Muto, S. Shimomura
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 42 (10) 2714 - 2717 1386-9477 2010/09 [Refereed][Not invited]
     
    Exciton spin and phase relaxations at low temperatures in GaAs/AlGaAs single quantum wells were investigated by using transient grating technique. The technique allows us to obtain the exciton lifetime, spin relaxation, and phase relaxation in the same setup. In combination with a series of single quantum wells grown on the same substrate, the well width dependence of exciton spin relaxation was studied. The obtained spin relaxation results were analyzed with their phase relaxation times in a framework of MAS mechanism, and were in good agreement with the calculated results. Especially, the motional narrowing character of the exciton spin relaxation was well demonstrated. (C) 2009 Elsevier B.V. All rights reserved.
  • R. Kaji, T. Shindo, S. Adachi, S. Muto
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 42 (10) 2501 - 2504 1386-9477 2010/09 [Refereed][Not invited]
     
    We demonstrated the circular to linear polarization conversion in single InAlAs/AlGaAs QDs. Since the anisotropic exchange interaction acts on the photo-created exciton spin as an in-plane effective magnetic field, the polarization of emissions can be converted from circular to linear and vice versa even under a zero external magnetic field. By using the quasi-resonant excitation, high conversion ratio up to similar to 50% was obtained under nonzero longitudinal magnetic field. Additionally, exciton spin relaxation time and built-in linear dichroism were estimated by exciton spin dynamics in the 3D pseudospin precession model. (C) 2010 Elsevier B.V. All rights reserved.
  • R. Kaji, S. Adachi, T. Shindo, S. Muto
    PHYSICAL REVIEW B 80 (23) 235334/1 - 6 1098-0121 2009/12 [Refereed][Not invited]
     
    The polarization conversion from optical orientation to alignment in single InAlAs/AlGaAs quantum dots (QDs) was studied in detail under zero and nonzero magnetic fields. Under the influence of the effective magnetic field, bright exciton doublets precess in pseudospin space, where the torque vector is composed of the external magnetic field and the anisotropic exchange field. For a number of QDs, we measured the angle difference of the polarization axes obtained with circularly polarized excitations, which is an indicator of the conversion efficiency under a zero magnetic field. By applying a longitudinal magnetic field, a high conversion efficiency of similar to 50% was achieved. Additionally, the exciton spin-relaxation time and the magnitude of built-in linear dichroism were estimated from the exciton spin dynamics using the three-dimensional pseudospin precession model, and a long spin-relaxation time exceeding the recombination lifetime was obtained. Finally, we discussed the influence of a nuclear magnetic field on the polarization conversion.
  • Y. Ueno, Y. Toda, S. Adachi, R. Morita, T. Tawara
    OPTICS EXPRESS 17 (22) 20567 - 20574 1094-4087 2009/10 [Refereed][Not invited]
     
    We demonstrate the coherent transfer of optical orbital angular momentum (OAM) to the center of mass momentum of excitons in semiconductor GaN using a four-wave mixing (FWM) process. When we apply the optical vortex (OV) as an excitation pulse, the diffracted FWM signal exhibits phase singularities that satisfy the OAM conservation law, which remain clear within the exciton dephasing time (similar to 1ps). We also demonstrate the arbitrary control of the topological charge in the output signal by changing the OAM of the input pulse. The results provide a way of controlling the optical OAM through carriers in solids. Moreover, the time evolution of the FWM with OAM leads to the study of the closed-loop carrier coherence in materials. (C) 2009 Optical Society of America
  • Tetsuro Ishiguro, Yasunori Toda, Satoru Adachi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (10) 104718/1-104718/4  0031-9015 2009/10 [Refereed][Not invited]
     
    We study the influence of the anisotropic exchange interaction (AEI) on exciton coherence by using four-wave-mixing spectroscopy. The exciton fine structure (FS) of uniaxially-strained GaN exhibits linearly-polarized FS-splitting at low temperatures, which enables us to resolve the difference between the coherent dynamics of the FS; the FWM transient in each FS exhibits extended/contracted dephasing compared with that obtained in uniformly-strained GaN. The origin of this asymmetry is associated with the anisotropic pseudospin induced by AEI.
  • H. Kumano, S. Ekuni, H. Kobayashi, H. Sasakura, I. Suemune, S. Adachi, S. Muto
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (4) 775 - 778 0370-1972 2009/04 [Refereed][Not invited]
     
    High degree of preservation of spin states mediated by optical phonons is demonstrated with a positive trion state in a single quantum dot. At the optical phonon resonance suppression of spin relaxation is clearly identified as a dip structures in photoluminescence excitation spectra under cross-circularly polarize detection with respect to a pumping. As a result, distinguishably high degree of circular polarization up to similar to 0.85 is achieved in the absence of external magnetic field, which is no the case for neutral excitons with finite fine structure splitting. The absence of continuum states plays a crucial role for this observation. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • H. Sasakura, S. Adachi, R. Kaji, K. Yamada, S. Muto
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (4) 784 - 787 0370-1972 2009/04 [Refereed][Not invited]
     
    We investigated an optically created nuclear field in a single InAlAs quantum dot and demonstrated that the zero effective electron g-factor could be achieved by the cancellation of the external magnetic field by the nuclear field at one edge of the nuclear polarization bistability. In addition, we discussed more practical way to realize the zero g-factor using the unique maximum value of the nuclear field, which keeps steady value against the fluctuation of excitation power. The cancellation for the electron Zeeman splitting provides the accurate hole g-factor. Since exciton g-factor is obtained by the Zeeman splitting without the nuclear field due to the linearly polarized excitation, we can evaluate the magnitudes and the signs of electron and hole g-factors in the growth direction of the single quantum dot. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • T. Ishiguro, Y. Toda, S. Adachi, K. Tadatomo, K. Hoshino
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 1 6 (1) 42 - + 1862-6351 2009 [Refereed][Not invited]
     
    Dephasing dynamics of exciton fine structure (EFS) caused by long and short range exchange interactions in GaN was investigated by using a four-wave-mixing (FWM) spectroscopy. The type of exchange interactions was selected by samples (uniaxially strained c-plane GaN films and a thick bulk GaN) and their geometries in optical excitation. Since each component of EFS is highly polarized, the polarization-dependent FWM spectra successfully resolve the dephasing dynamics in the individual EFS resonances. The results show a difference in dephasing time, suggesting a contribution of anisotropic exchange interaction (AEI). (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • H. Sasakura, S. Adachi, R. Kaji, S. Muto
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 4 6 (4) 837 - + 1862-6351 2009 [Refereed][Not invited]
     
    We demonstrated the creation of nanoscale magnetic field into the two isolated semiconductor quantum dots in spatially-confined mesa structure of similar to 150 nm diameter using an optical pumping of the nuclear spins. The amplitude of nuclear field between two isolated quantum dots under same pumping condition were clearly difference, suggesting that the nanoscale-locality of the nuclear field was found to be around 100 nm. This method is based on the sensitivity of the critical magnitudes of the external magnetic field to the quantum dot properties in the bistable behavior of nuclear spin polarization. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Y. Toda, K. Yamaguchi, T. Ishiguro, K. Hoshino, K. Tadatomo, S. Adachi
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, SUPPL 2 6 S684 - S686 1862-6351 2009 [Refereed][Not invited]
     
    Spatial imaging of spectrally-resolved four-wave mixing (SR FWM) was performed on a GaN film grown on c-sapphire substrate. The image obtained from the exciton resonances at zero time delay clearly showed some highly localized reductions in their intensities whose spatial profiles can be mapped out with a spatial resolution of similar to 20 m. The image obtained from the evaluation of the quantum beats indicates these reductions correspond to the phase changes between two exciton transitions, reflecting the spatial properties of exciton-exciton interactions. The line-localization suggests a contribution of line-defect to the anomalous interactions. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • T. Ishiguro, Y. Toda, S. Adachi, S. F. Chichibu
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, SUPPL 2 6 S719 - S722 1862-6351 2009 [Refereed][Not invited]
     
    We report on the dephasing dynamics of exciton fine structure (EFS) in a free standing GaN. The EFS was observed and studied by utilizing a four-wave-mixing (FWM) spectroscopy. In the cleavage plane of wurtzite GaN, we can excite the B-exciton fine structure, whose z-polarized state is energetically well separated from the other in-plane polarized exciton states. Due to the large spin exchange interaction in GaN, an energy shift of in-plane polarized fine structure was also observed. Since the each component of EFS is highly polarized, the polarization-dependent FWM successfully resolves their dephasing dynamics. The results show a significant difference in the dephasing time between EFS, suggesting that anisotropic exchange interaction is effective as reported in our previous work using a GaN film on alpha-plane sapphire. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • R. Kaji, K. Yamada, H. Sasakura, S. Adachi
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 245 (12) 2662 - 2666 0370-1972 2008/12 [Refereed][Not invited]
     
    Precise optical evaluation of electron and hole g-factors in single InAlAs quantum dot was performed by using the optical pumping of nuclear magnetic field and its bistable behavior. The measurement is based on the fact that the induced nuclear field is effective only on electrons and can compensate the external magnetic field. The experimental results indicate that the effective electron g-factor can change in large magnitude including the sign in a controllable manner. Therefore, the method will be useful for the spin manipulation experiments such as photon-spin qubit conversion. In addition, the in-plane electron and hole g-factors were measured in Voigt geometry. This is the first report of individual g-factors of electron and hole in single InAlAs/AlGaAs quantum dots, which have been reported so far by only a few studies about the exciton g-factor. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • H. Kumano, H. Kobayashi, S. Ekuni, Y. Hayashi, M. Jo, H. Sasakura, S. Adachi, S. Muto, I. Suemune
    PHYSICAL REVIEW B 78 (8) 081306(R)/1 - 4 1098-0121 2008/08 [Refereed][Not invited]
     
    High degree of excitonic spin-state preservation during energy relaxation is demonstrated in a single quantum dot. Optical-phonon resonances and corresponding suppression of spin relaxation are clearly identified as dip structures in photoluminescence excitation spectra probed by the positive trion emission. Consequently, under the longitudinal optical-phonon resonant excitation, a distinguishably high degree of circular polarization up to similar to 0.85 is achieved. Extended spin-relaxation time in the positive trion ground state compared to that in neutral exciton ground state is also revealed.
  • H. Sasakura, S. Adachi, S. Muto, S. Hirose, H. Z. Song, M. Takatsu
    JOURNAL OF APPLIED PHYSICS 103 (10) 103530/1 - 5 0021-8979 2008/05 [Refereed][Not invited]
     
    The oscillations of excitonic and nuclear spin polarizations in an optically pumped single self-assembled In0.8Al0.2As/Al0.35Ga0.65As quantum dot (QD) were clearly observed under the excitation of a wetting layer edge at B=5 T. This indicates that an exciton pair with opposite spins is alternatively created via the half-localized state only by changing the delay time between cross-linearly polarized pulse pair. Furthermore, periodic modulation of Zeeman energy synchronizes the degree of circular polarization of photoluminescence from a single QD, indicating that the Overhauser field follows the optically created electron spin polarization in half-localized states of a QD, and the half-localized state in a QD consists of a confined electron in a discrete state and hole in the continuum state. (C) 2008 American Institute of Physics.
  • Y. Toda, T. Ishiguro, S. Adachi, K. Hoshino, K. Tadatomo
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 245 (5) 878 - 880 0370-1972 2008/05 [Refereed][Not invited]
     
    We have previously demonstrated that a spectrally-resolved four-wave mixing highlights the anisotropically polarized excitons in the uniaxially strained GaN films [1], where the enhancement of sensitivity for an uniaxial strain, was achieved by nonlinear response of the exciton polarization. In this work, we have applied this technique to the GaN films on various substrates including isotropic ones, and have examined the sensitivity of the technique. The results show distinct polarizations and energy variations originating from the uniaxial strain, the magnitude of which depends on the sample and its position: The minimum changes of the polarized FWM intensity and exchange energy splittings correspond to a uniaxial strain of 5.0 x 10(-5), which currently gives a lower resolution limit of this technique. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • H. Kumano, H. Kobayashi, Y. Hayashi, M. Jo, I. Suemune, H. Sasakura, S. Adachi, S. Muto
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 40 (6) 1824 - 1827 1386-9477 2008/04 [Refereed][Not invited]
     
    Single photon emission with high degree of circular polarization (DCP) from a positively charged exciton (trion) state in a single quantum dot (QD) is demonstrated under zero magnetic field. Obtained high DCP as large as 0.6 is a clear manifestation of highly effective mutual polarization conversion between single photon and single electron spin. This finding also reveals that the spin relaxation is strongly suppressed during capture and thermalization processes and also in trion ground states in a QD. Moreover, exciton charging state control is shown to be possible by modifying the electron capture probability through the excitation energy tuning, which leads to an exclusive formation of the positive trion in a QD. (c) 2007 Published by Elsevier B.V.
  • R. Kaji, S. Adachi, H. Sasakura, S. Muto
    PHYSICAL REVIEW B 77 (11) 115345/1 - 5 1098-0121 2008/03 [Refereed][Not invited]
     
    Optically pumped nuclear spin polarization in single InAlAs quantum dots was investigated in detail with regards to the dependences on the excitation power and electron spin polarization. By increasing (or decreasing) the excitation power at a particular excitation polarization, an abrupt rise (or drop) and a clear hysteretic behavior were observed in the Overhauser shift of the photoluminescence under an external magnetic field of 5 T. Those features appear equivalently for the exciton and exciton complexes of the same quantum dot since the created nuclear field is equally effective. However, the degree of circular polarization shows different behaviors between a positively charged exciton and a neutral exciton or biexciton; further, only the positively charged exciton exhibits the precisely synchronized change and hysteretic behavior. It is suggested that the electron spin distribution is affected by the flip-flop of electron-nuclear spins. Further, the hysteresis is observed as a function of the degree of circular polarization of the excitation light, and its dependence on the excitation power is studied. The saturation of the Overhauser shift indicates the almost complete cancellation of the external magnetic field by the nuclear field.
  • H. Kobayashi, H. Kumano, M. Endo, M. Jo, I. Suemune, H. Sasakura, S. Adachi, S. Muto
    MICROELECTRONICS JOURNAL 39 (3-4) 327 - 330 0026-2692 2008/03 [Refereed][Not invited]
     
    Origin of sharp photoluminescence lines observed from an InAlAs quantum dot was identified with the measurements of excitation-power dependences and polarization correlations, together with photon correlation measurements. Single photon emission with high degree of circular polarization (DCP) up to 60% was observed from a positively charged exciton (trion) state in the single quantum dot under non-resonant excitation at zero magnetic field. (C) 2007 Elsevier Ltd. All rights reserved.
  • R. Kaji, H. Sasakura, S. Adachi, S. Muto
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 1 5 (1) 298 - + 1862-6351 2008 [Refereed][Not invited]
     
    In a single self-assembled InAlAs quantum dot, we report the nonlinearity of nuclear spin polarization by optical pumping. Increasing (or decreasing) the excitation power at a particular excitation polarization, nuclear spin polarization shows the abrupt jump (or drop) and a clear hysteresis loop. In addition, the degree of circular polarization of positively charged exciton also exhibits similar bistable behavior and the hysteretic operation has the precise synchronization with the nuclear spin polarization. It suggests that an electron in the positively charged exciton plays a main role to create the abrupt change of the nuclear spin polarization in the observed quantum dot. This abrupt change reveals the sign and magnitude of the electron g-factors in z-direction and can be explained by using a simple model calculation. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S. Adachi, H. Sasakura, N. Yatsu, R. Kaji, K. Yamada, S. Muto, H. Kumano, I. Suemune
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 1 5 (1) 351 - + 1862-6351 2008 [Refereed][Not invited]
     
    We report the photon-correlation Fourier spectroscopy of exciton and exciton complexes in single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dots. A Michelson interferometer inserted in the photoluminescence path was used to measure the coherent length of the time-averaged emission of neutral exciton, biexciton, and positive trion. As comparing with their coherence time and their excitation energy dependence, the effects of the exchange interaction and the fluctuation of the surrounding excess charge are discussed.
  • T. Ishiguro, Y. Toda, S. Adachi, K. Hoshino, Y. Arakawa
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 6 5 (6) 2114 - + 1862-6351 2008 [Not refereed][Not invited]
     
    Dephasing dynamics of excitons in a GaN film grown on a-plane sapphire were studied by using the spectrally-resolved four-wave-mixing (SR-FWM) spectroscopy. Due to the anisotropic exchange interaction originates from the anisotropic strain field of the substrate, the degenerate exciton states with the total angular moment +/- 1 mix and split into their fine structures. Since each component of the exciton fine structured (EFS) is highly polarized, the polarization-dependent SR-FWM spectra successfully resolve the dephasing dynamics in the individual EFS resonances. The result of each EFS shows a significantly different dephasing time, suggesting that the anisotropic dephasing contribution occurs in each EFS.
  • H. Sasakura, R. Kaji, S. Adachi, S. Muto
    APPLIED PHYSICS LETTERS 92 (4) 041915/1 - 3 0003-6951 2008/01 [Refereed][Not invited]
     
    We investigated an optically created nuclear field in a single InAlAs quantum dot and demonstrated that the nuclear field can be used to discriminate whether photoluminescence lines originate from the same dot or a different dot. Since the nonlinear response of the nuclear field is sensitive to the electron g factor and correlation time of a coupled electron-nuclear spin system, the resultant Overhauser shift is their good measure for individual quantum dots. This method provides a simple and convenient alternative to the standard photon cross-correlation method. (c) 2008 American Institute of Physics.
  • T. Ishiguro, Y. Toda, S. Adachi, S. F. Chichibu
    ULTRAFAST PHENOMENA IN SEMICONDUCTORS AND NANOSTRUCTURE MATERIALS XII 6892 689219/1 - 11 0277-786X 2008 [Not refereed][Not invited]
     
    We perform degenerate four-wave-mixing (FWM) studies of GaN excitons especially for an understanding of the strain-fields in the heteroepitaxial films. The shifts of exciton energies and their beating oscillation variations highlight the biaxial strain, allowing for a precise determination of the strain parameters. The uniaxial strain field can be characterized by the polarization dependence of FWM, which shows distinct polarizations and energy variations depending on the sample and its position. The minimum changes of the polarized FWM intensity and exchange energy splittings correspond to a uniaxial strain of 5.0 x 10(-5). which currently gives a lower resolution limit of this technique and is comparable with that of conventional X-ray diffraction. In the time-evolutions, we investigate the strain effects on the phase of the quantum beats (QBs), giving insight into the excitons interactions. By using time-resolved FWM, difference between two-types of exciton transitions is identified. In addition, coherent manipulations of QBs are successfully realized in the FWM with a Michelson interferometer.
  • R. Kaji, S. Adachi, H. Sasakura, S. Muto
    APPLIED PHYSICS LETTERS 91 (26) 261904/1 - 3 0003-6951 2007/12 [Refereed][Not invited]
     
    We demonstrated the cancellation of the external magnetic field by the nuclear field at one edge of the nuclear polarization bistability in single InAlAs quantum dots. The cancellation for the electron Zeeman splitting gives the precise value of the hole g factor. In combination with the exciton g factor that is obtained from the Zeeman splitting for linearly polarized excitation, the magnitude and the sign of the electron and hole g factors in the growth direction are evaluated. (c) 2007 American Institute of Physics.
  • S. Adachi, N. Yatsu, R. Kaji, S. Muto
    APPLIED PHYSICS LETTERS 91 (16) 161910/1 - 3 0003-6951 2007/10 [Refereed][Not invited]
     
    We report the single-photon Fourier spectroscopy of exciton and exciton complexes in single self-assembled InAlAs/AlGaAs quantum dots. A Michelson interferometer was inserted in the photoluminescence path for measuring the coherence length of the time-averaged emission of neutral excitons and their complexes. The effects of exchange interactions and fluctuations in the surrounding excess charges were estimated by comparing the coherence times and the excitation energies of the excitons and their complexes. (C) 2007 American Institute of Physics.
  • R. Kaji, S. Adachi, H. Sasakura, S. Muto, H. Kumano, I. Suemune
    JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 20 (6) 447 - 451 1557-1939 2007/08 [Refereed][Not invited]
     
    We investigated optical pumping of nuclear spin polarizations in a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot. The nuclear spin polarization exhibits the abrupt jump and hysteresis in the excitation power dependence at a particular excitation polarization. Measurement of circular polarization rate of the photoluminescence reveals that the abrupt change of the nuclear spin polarization is created mainly by the spin flip-flop process between nuclei and an electron of a positive charged exciton in this single quantum dot. Model calculation explains well the experimentally observed bistable behavior in InAlAs quantum dot. By using this abrupt change, the sign and magnitude of electron and hole g-factors in z-direction are verified.
  • H. Sasakura, S. Kayamori, S. Adachi, S. Muto
    JOURNAL OF APPLIED PHYSICS 102 (1) 013515/1 - 4 0021-8979 2007/07 [Refereed][Not invited]
     
    The control of the emission energy from self-assembled InAs quantum dots has been demonstrated by using indium flush. The low-temperature indium-flush method was found to control the emission energy preserving the high structural uniformity attributed to the slow dot growth. In the standard indium-flush method, where the substrate temperature was raised up from the dot-growth temperature, blueshift larger than the shift by the low-temperature indium flush was observed and was explained reasonably by the enhanced In/Ga-interdiffusion. Also, the effect of AlGaAs capping layer before the indium-flush step was studied. (c) 2007 American Institute of Physics.
  • T. Ishiguro, Y. Toda, S. Adachi, K. Hazu, T. Sota, S. F. Chichibu
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4 NO 7 2007 4 (7) 2776 - + 1862-6351 2007 [Refereed][Not invited]
     
    An optical coherent manipulation of excitonic polarizations in hexagonal bulk GaN is achieved by means of an interferometric technique combined with spectrally-resolved degenerate four-wave-mixing (FWM). Initial phase of the FWM quantum beats between A and B excitonic polarizations are arbitrarily controlled, in which simultaneous increase (decrease) of the beats in both polarizations are observed. In addition, 80% selective amplification and 40% suppression of one of the excitonic polarizations are realized.
  • T. Ishiguro, Y. Toda, S. Adachi
    APPLIED PHYSICS LETTERS 90 (1) 011904/1 - 3 0003-6951 2007/01 [Refereed][Not invited]
     
    The authors studied the exciton spin relaxation of bulk GaN by creating spin polarization gratings using degenerate four-wave mixing spectroscopy. The spectrally resolved analysis achieved with this technique facilitated the direct evaluation of spin polarizations in the individual excitons (A and B excitons). The spin polarizations for each exciton decay very quickly (tau(s)similar to 1 ps) at low temperatures. Moreover the tau(s) is faster than the dephasing time T-2 throughout the measured temperature range, suggesting the existence of fast intrinsic spin relaxation processes, which can be attributed to a large exchange constant characterized in GaN.
  • K. Yamaguchi, Y. Toda, T. Ishiguro, S. Adachi, K. Hoshin, K. Tadatomo
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4 NO 7 2007 4 (7) 2752 - + 1862-6351 2007 [Refereed][Not invited]
     
    Quantum beats in the time-resolved four-wave mixing (FWM) signals arising from GaN excitons are observed. Two different types of beats are investigated: beats between the A-exciton (X-A) and B-exciton (X-B) states; beats between the XA and A-biexciton ((XXA)) states. The former exhibits oscillations along all directions in the delay- (T) and real-time (t) plane while the latter exhibits no beat in the direction parallel to the diagonal axis (T = t). The results are well reproduced by a model calculation, showing good homogeneity of the sample.
  • T Ishiguro, Y Toda, S Adachi, M Arita, Y Arakawa
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 243 (7) 1564 - 1567 0370-1972 2006/06 [Refereed][Not invited]
     
    We have studied exciton spin relaxation in strained GaN epilayers on various sapphire substrates using spin-dependent transient reflectivity and three-pulse four-wave mixing measurements. Strikingly fast exciton spin relaxation (< 1 ps) at 10 K was observed in the lowest exciton level (A-exciton) both in bulk and GaN layer on c-sapphire. In contrast, the transient signals in the GaN layer on alpha-sapphire show the break down of the spin polarization caused by the exchange interaction.
  • T Ishiguro, Y Toda, S Adachi, T Mukai, K Hoshino, Y Arakawa
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 243 (7) 1560 - 1563 0370-1972 2006/06 [Refereed][Not invited]
     
    We have carried out time-integrated and spectrally-resolved four-wave mixing (FWM) measurements to study the effects of built-in strain within GaN films on their exciton structures and on their coherent dynamics. Precise values for exciton energies, linewidths, and oscillation periods of quantum beats were presented. Remarkable phase shifts of the quantum beats were observed in the GaN films on a-sapphire, suggesting the exciton-exciton interaction caused by the reduction of the crystal symmetry.
  • Satoru Adachi, Yasunori Toda, Tetsuro Ishiguro
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 243 (7) 1568 - 1571 0370-1972 2006/06 [Refereed][Not invited]
     
    Biexcitons of GaN under uniaxial strain have been investigated by spectrally-resolved four-wave mixing (FWM) technique. Two kinds of biexcitons were observed clearly and the binding energies were obtained. Since the uniaxial strain changes the exciton structure, the biexciton binding is modified and biexciton has also fine structure, which was revealed in the FWM spectra that were obtained by rotating the linearly polarized excitation against the direction of uniaxial strain.
  • Hidekazu Kumano, Satoshi Kimura, Michiaki Endo, Ikuo Suemune, Hirotaka Sasakura, Satoru Adachi, Shunichi Muto, Hai Zhi Song, Shinichi Hirose, Tatsuya Usuki
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 32 (1-2) 144 - 147 1386-9477 2006/05 [Refereed][Not invited]
     
    Triggered single-photon generation from InAlAs quantum dot (QD) was demonstrated for the first time. Emitted photon energy coincides with high detection efficiency range of Si single-photon detectors, which is highly suitable for free-space communication. Single-QD spectroscopy and crossed photon correlation measurements unambiguously revealed that several emitting lines observed in a single mesa structure originated from the identical QD, and two temporary competing decay processes associated with neutral states and charged states were identified. Presence of the competing process is also inferred from an analysis of steady-state photoluminescence intensities. Formation process of charged exciton in QD is also discussed. (c) 2006 Elsevier B.V. All rights reserved.
  • Hidekazu Kumano, Satoshi Kimura, Michiaki Endo, Hirotaka Sasakura, Satoru Adachi, Shunichi Muto, Ikuo Suemune
    JOURNAL OF NANOELECTRONICS AND OPTOELECTRONICS 1 (1) 39 - 51 1555-130X 2006/04 [Refereed][Not invited]
     
    Photon emission with nonclassical photon statistics is discussed with a single InAlAs quantum dot. The deterministic single-photon generation in which the emitted photon wavelength matches well to the highly sensitive wavelength region of highly efficient, low-noise Si-single-photon detectors and also to an atmospheric transmission window is demonstrated. Competing transition processes between neutral and charged exciton species originating from an exclusive formation in the same single quantum dot are clarified. It was found that suppressing the charged exciton formation is possible by a quasi-resonant excitation for a deterministic monochromatic single-photon generation. Polarization-dependent photoluminescence spectroscopy clearly indicates the preservation of photon polarizations between photons emitted by biexciton/exciton recombinations. Furthermore, the deterministic polarization-correlated photon pair generation with biexciton-exciton cascaded transition occurring in a single quantum dot is directly confirmed by the polarized second-order photon correlation measurements. This indicates a longer polarization flip time than the exciton lifetime, which is an essential requirement for the deterministic Einstein-Podolsky-Rosen photon pair generation under the present biexciton-exciton cascaded transition scheme.
  • H. Nishida, S. Kayamori, H. Sasakura, S. Adachi, S. Muto, I. Suemune
    Physica Status Solidi (C) Current Topics in Solid State Physics 3 (12) 4299 - 4302 1862-6351 2006 [Refereed][Not invited]
     
    We have investigated the influence of postgrowth thermal annealing on the optical properties of InAs/GaAs self-assembled quantum dots. Upon annealing, the emission from InAs QDs shifts toward higher energies with a narrowing of the photoluminescence spectra of QD ensemble. The time-integrated PL spectra show also the nonradiative recombination rate does not increase by annealing process. In addition, from the timeresolved PL, the exciton radiative recombination rate increases with increasing the annealing temperature and agrees well with the atomic-like radiative recombination. These results indicate that interdiffusion of Ga and In atoms into and out of the QDs leads to an increase of the average dot size and concurrently a decrease in the confinement potentials of the QDs preserving their optical quality and zero-dimensional density of states after interdiffusion in the studied annealing temperature range. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
  • T. Mukumoto, R. Kaji, H. Sasakura, S. Adachi, H. Kumano, S. Muto, I. Suemune
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 12 3 (12) 4372 - 4375 1862-6351 2006 [Refereed][Not invited]
     
    We report optical pumping of nuclear spin polarization in a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot where the exciton has a fine structure. Through the change of state mixing that is induced by the anisotropic exchange interaction and the applied magnetic field, the relationship between the magnitude of the Overhauser shift and the optically injected electron spin polarization is discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Shinji Abe, Hirotaka Sasakura, Satoru Adachi, Shunichi Muto
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 12 3 (12) 4295 - 4298 1862-6351 2006 [Refereed][Not invited]
     
    We have investigated the pulse parameters of the stimulated Raman adiabatic passage (STIRAP) for efficient electron transfer in the coupled quantum dot system, and we found that STIRAP is sensitive to the difference between the dipole moments of the involved transitions. We have designed the QD structures where this drawback can be suppressed, to show the practicality of the photon-assisted tunneling between spatially-separated QDs. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Satoru Adachi, Yasunori Toda, Tetsuro Ishiguro, Katsuyuki Hoshino, Yasuhiko Arakawa
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 6 3 (6) 1595 - 1598 1862-6351 2006 [Refereed][Not invited]
     
    Exciton fine structures induced by the uniaxial strain have been revealed in gallium nitride grown on an a-plane sapphire substrate by using the spectrally-resolved four-wave mixing technique. Sensitivity on the exciton polarization is enhanced by the nonlinearities of the four wave mixing signals, and therefore the safety alternative tool for mapping of the uniaxial strain field and the resultant anisotropic exchange can be offered. Such a nonlinear spectroscopic measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • I. Suemune, H. Kumano, S. Kimura, H. Sasakura, S. Adachi, S. Muto, H. Z. Song, S. Hirose, T. Usui
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 11 3 (11) 3908 - + 1862-6351 2006 [Refereed][Not invited]
     
    It is well-recognized that exciton-state energy splitting makes it difficult to generate entangled photon pairs (EPP) from a single quantum dot (QD). It will be shown that the splitting of the exciton states originates from not only QD anisotropy but also ionization of residual impurities. This result shows that the growth of highly pure barrier layers will be necessary for the generation of EPP. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • T Yokoi, S Adachi, S Muto, H Sasakura, HZ Song, S Hirose, T Usuki
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 29 (3-4) 510 - 514 1386-9477 2005/11 [Refereed][Not invited]
     
    We report the polarization-dependent energy shift of excitonic emission in a self-assembled InAlAs/AlGaAs quantum dot (QD). The energy shift is well known as Overhauser shift and was observed in a naturally formed GaAs QD using monolayer fluctuation of a quantum well. However, there has been no observation so far in a self-assembled QD, which is suitable for formation of vertically coupled QDs. We demonstrate that the magnitude of the Overhauser shift is enhanced by the photo-injection of the highly polarized electron and is controllable by the polarization of the excitation light in a self-assembled InAlAs QD. (c) 2005 Elsevier B.V. All rights reserved.
  • S Muto, S Adachi, T Yokoi, H Sasakura, Suemune, I
    APPLIED PHYSICS LETTERS 87 (11) 112506/1 - 3 0003-6951 2005/09 [Refereed][Not invited]
     
    We propose a method to realize the conversion of photon qubit and spin qubit using the effective magnetic field created by the nuclear polarization known as Overhauser field. We discuss the preliminary experiment on an InAlAs/AlGaAs self-assembled quantum dot and also discuss the effects of electron-hole interaction on the conversion. (c) 2005 American Institute of Physics.
  • Y Toda, S Adachi, Y Abe, K Hoshino, Y Arakawa
    PHYSICAL REVIEW B 71 (19) 195315/1 - 5 1098-0121 2005/05 [Refereed][Not invited]
     
    The degenerate four-wave mixing (FWM) spectroscopy of uniaxially strained GaN layers is demonstrated using colinearly polarized laser pulses. The nonlinear response of FWM signal on exciton oscillator strength enhances the sensitivity for polarized exciton, allowing for mapping out the in-plane anisotropy of the strain field. The observed high-contrast spectral polarization clearly shows fine structure splittings of excitons, which are also confirmed in the change of quantum beating periods of time.
  • S Adachi
    JOURNAL OF LUMINESCENCE 112 (1-4) 34 - 39 0022-2313 2005/04 [Refereed][Not invited]
     
    We have investigated free excitons and biexcitons of bulk ZnO by time-integrated and spectrally resolved four-wave mixing (FWM). The polarization- and wave-vector-dependent FWM signals for A and B excitons demonstrate clearly that the valence-band ordering is A-Gamma(9), B-Gamma(7), and C-Gamma(7). Also, we gave qualitative explanation of the FWM signals induced by excitons and biexcitons in ZnO. For negative delay times, bound and unbound AB-biexcitons (A exciton-B exciton correlation), which have been considered to play a minor role in GaAs hetero structures, was found to play an important role and give a significant qualitative impact to the optical response of ZnO. (c) 2004 Elsevier B.V. All rights reserved.
  • K Hazu, S Adachi, T Sota, SF Chichibu
    JOURNAL OF LUMINESCENCE 112 (1-4) 7 - 10 0022-2313 2005/04 [Refereed][Not invited]
     
    We have studied the exciton-polariton dynamics in a c-face bulk ZnO crystal grown by the seeded vapor transport method. We have performed two-pulse spectrally resolved four-wave mixing (SR-FWM) and three-pulse SR-FWM at T = 10 K. In two-pulse FWM experiment, obtained FWM signals showed the fast dephasing which has been attributed to the strong polariton dispersion of the upper polariton of B exciton. On the other hand, in three-pulse FWM experiment, the signal decay shows the free exciton population relaxation. Observed FWM signal has decayed with time constant similar to 12 ps which may represent exciton-polariton lifetime. (c) 2004 Elsevier B.V. All rights reserved.
  • T Watanuki, S Adachi, H Sasakura, S Muto
    APPLIED PHYSICS LETTERS 86 (6) 063114/1 - 3 0003-6951 2005/02 [Refereed][Not invited]
     
    Exciton spin relaxation in self-assembled InAlAs quantum dots was investigated by three-pulse four-wave mixing under resonant conditions. The concept of the spin grating holds well for quantum dots and the measurements combined with optical heterodyne detection at 10 K demonstrates that the exciton spin relaxation lasts up to a few nanoseconds and the time constant is similar to5 times larger than the exciton recombination time on average. (C) 2005 American Institute of Physics.
  • S Adachi, Y Toda
    PHYSICA STATUS SOLIDI C - CONFERENCES AND CRITICAL REVIEWS, VOL. 2 , NO 11 2 (11) 3936 - 3940 1862-6351 2005 [Refereed][Not invited]
     
    Spectrally-resolved four-wave mixing technique has revealed the internal structures of excitons in uniaxially strained gallium nitride films. Nonlinear response of four-wave mixing on the oscillator strength highlights the polarized excitons, and therefore allows us to map out the uniaxial strain field and the resultant anisotropic exchange splitting. Such a measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics.
  • S Kimura, H Kumano, M Endo, Suemune, I, T Yokoi, H Sasakura, S Adachi, S Muto, HZ Song, S Hirose, T Usuki
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 (24-27) L793 - L796 0021-4922 2005 [Refereed][Not invited]
     
    Single-photon emitters and detectors are key devices to realize secure communications with single-photon-based quantum cryptography and single-photon-based quantum computing. InAlAs quantum dots (QDs) cover the wavelength range with high quantum efficiencies of Si-based single-photon detectors. Clear photon antibunching was observed from an InAlAs single QD under weak excitations. To realize single-photon emitters on demand, complete population of the QD energy states before the photon emission events is necessary, but the measured antibunching properties were dependent substantially on the photo-excitation powers. The physical origin of this problem is discussed. The criterion to distinguish the real deviation from the photon antibunching condition and the artifact of the measurements is clarified. The capability of single-photon emissions on demand will be demonstrated with photon antibunching under pulsed operations.
  • S Kimura, H Kumano, M Endo, Suemune, I, T Yokoi, H Sasakura, S Adachi, S Muto, HZ Song, S Hirose, T Usuki
    PHYSICA STATUS SOLIDI C - CONFERENCES AND CRITICAL REVIEWS, VOL. 2 , NO 11 2 (11) 3833 - 3837 1862-6351 2005 [Refereed][Not invited]
     
    Regulated single-photon generation from an InAlAs quantum dot was demonstrated at a wavelength in which Si-avalanche photodiode single-photon detector has high quantum efficiency. Measured excitation power dependence of photon coincidence counts revealed that highly pure single-photon emission was realized at low excitation powers. Beyond a critical excitation, population of multi-exciton states in the quantum dot degraded the purity of single-photon emission. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S Adachi, K Hazu, T Sota, S Chichibu, G Cantwell, DC Reynolds, CW Litton
    FOURTH INTERNATIONAL CONFERENCE ON PHYSICS OF LIGHT-MATTER COUPLING IN NANOSTRUCTURES (PLMCN4) 2 (2) 890 - 895 1862-6351 2005 [Refereed][Not invited]
     
    We have investigated free excitons and biexcitons of bulk ZnO by time-integrated and spectrally-resolved four-wave mixing. The polarization- and wave-vector-dependent FWM signals for A and B excitons demonstrate clearly that the valence-band ordering is A - Gamma(9), B - Gamma(7), and C - Gamma(7). Next, we gave qualitative explanation of the FWM signals induced by excitons and biexcitons in ZnO. For negative delay times, bound and unbound AB-biexcitons (A exciton-B exciton correlation), which have been considered to play a minor role in GaAs heterostructures, was found to play an important role and give a significant qualitative impact to the optical response of ZnO. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S Adachi, T Watanuki, H Sasakura, S Muto
    Fourth International Conference on Physics of Light-Matter Coupling in Nanostructures (PLMCN4) 2 (2) 854 - 857 1610-1634 2005 [Refereed][Not invited]
     
    Exciton spin relaxation in self-assembled InAlAs quantum dots were investigated by three-pulse four-wave mixing under resonant conditions. The concept of the spin grating holds well for quantum dots and the measurements combined with optical heterodyne detection at 10 K demonstrates that the exciton spin relaxation last up to a few ns and the time constant is similar to 5 times larger than the exciton recombination time in average. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • T Yokoi, S Adachi, H Sasakura, S Muto, HZ Song, T Usuki, S Hirose
    PHYSICAL REVIEW B 71 (4) R041307/1 - 4 1098-0121 2005/01 [Refereed][Not invited]
     
    We report optical spectroscopic results of a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot. The polarization-dependent shift of the Zeeman splitting in a single InAlAs quantum dot (QD) has been observed. The induced Overhauser field is estimated to be similar to0.16 T in this InAlAs QD and the magnitude is shown to be controllable by the degree of circular polarization of excitation light.
  • S Adachi, T Yokoi, H Sasakura, S Muto, H Kumano, Suemune, I
    PHYSICA STATUS SOLIDI C - CONFERENCES AND CRITICAL REVIEWS, VOL. 2 , NO 11 2 (11) 3838 - 3842 1862-6351 2005 [Refereed][Not invited]
     
    We present the signature for optical pumping of nuclear spins in a self-assembled InAlAs/AlGaAs quantum dot via the polarization-dependent energy shift of the excitonic emission. The energy shift is well known as Overhauser shift and has observed in a interface-fluctuation GaAs quantum dot. However, there has been no observation so far in a self-assembled QD, which is suitable for formation of vertically coupled QDs. We have demonstrated that the magnitude of the Overhauser shift was enhanced by the photo-injection of the highly-polarized electron and was controllable by the polarization of the excitation light. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Satoru Adachi, Tomonori Yokoi, Hirotaka Sasakura, Shunichi Muto, Hidekazu Kumano, Ikuo Suemune
    Physica Status Solidi C: Conferences 2 (11) 3838 - 3842 1610-1634 2005 [Refereed][Not invited]
     
    We present the signature for optical pumping of nuclear spins in a self-assembled InAlAs/AlGaAs quantum dot via the polarization-dependent energy shift of the excitonic emission. The energy shift is well known as Overhauser shift and has observed in a interface-fluctuation GaAs quantum dot. However, there has been no observation so far in a self-assembled QD, which is suitable for formation of vertically coupled QDs. We have demonstrated that the magnitude of the Overhauser shift was enhanced by the photo-injection of the highly-polarized electron and was controllable by the polarization of the excitation light. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S. Kimura, H. Kumano, M. Endo, I. Suemune, T. Yokoi, H. Sasakura, S. Adachi, S. Muto, H. Z. Song, S. Hirose, T. Usuki
    Physica Status Solidi C: Conferences 2 (11) 3833 - 3837 1610-1634 2005 [Refereed][Not invited]
     
    Regulated single-photon generation from an InAlAs quantum dot was demonstrated at a wavelength in which Si-avalanche photodiode single-photon detector has high quantum efficiency. Measured excitation power dependence of photon coincidence counts revealed that highly pure single-photon emission was realized at low excitation powers. Beyond a critical excitation, population of multi-exciton states in the quantum dot degraded the purity of single-photon emission. ©2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Satoru Adachi, Yasunori Toda
    Physica Status Solidi C: Conferences 2 (11) 3936 - 3940 1610-1634 2005 [Refereed][Not invited]
     
    Spectrally-resolved four-wave mixing technique has revealed the internal structures of excitons in uniaxially strained gallium nitride films. Nonlinear response of four-wave mixing on the oscillator strength highlights the polarized excitons, and therefore allows us to map out the uniaxial strain field and the resultant anisotropic exchange splitting. Such a measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • K Hazu, T Sota, S Adachi, S Chichibu, G Cantwell, DC Reynolds, CW Litton
    JOURNAL OF APPLIED PHYSICS 96 (2) 1270 - 1272 0021-8979 2004/07 [Refereed][Not invited]
     
    The phase relaxation time of biexcitons T-2(bi) and that of excitons T-2(ex) in a bulk ZnO have been measured by the use of femtosecond four-wave mixing as functions of excitation wavelength, excitation power, and temperature. The biexciton-acoustic phonon interaction coefficient has been determined to be beta(ac)(bi)approximate to53 mueV/K as an average value. For A excitons, the interaction coefficients with acoustic and optical phonons have been determined to be beta(ac)(ex)approximate to8.4 mueV/K and beta(opt)(ex)approximate to14 meV, respectively. (C) 2004 American Institute of Physics.
  • K Hazu, K Torii, T Sota, S Adachi, SF Chichibu, G Cantwell, DC Reynolds, CW Litton
    JOURNAL OF APPLIED PHYSICS 95 (10) 5498 - 5501 0021-8979 2004/05 [Refereed][Not invited]
     
    Time-integrated and spectrally resolved four-wave mixing (FWM) has been applied to study the impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO. From the excitation wavelength dependence of the FWM signal, we have found possible evidence that the mixing of the Gamma(1) and Gamma(5L) states leads to a three-branch excitonic polariton dispersion but the oscillator strength transfer is small. The energy separation between the lower polariton branch and the extra branch due to the k-linear term has been found to be 3.5 meV. In addition, a binding energy of biexcitons consisting of two C excitons of 1.4 meV has been obtained. (C) 2004 American Institute of Physics.
  • S Adachi, K Hazu, T Sota, SF Chichibu, G Cantwell, DB Eason, DC Reynolds, CW Litton
    SEMICONDUCTOR SCIENCE AND TECHNOLOGY 19 (4) S276 - S278 0268-1242 2004/04 [Refereed][Not invited]
     
    We demonstrate that exciton-exciton correlations strongly affect FWM signals. In particular, A exciton-B exciton correlation (bound and unbound A B-biexcitons), which can be generated even in co-circular polarizations, has a significant qualitative impact on the optical response of bulk ZnO.
  • H Sasakura, S Adachi, S Muto, T Usuki, M Takatsu
    SEMICONDUCTOR SCIENCE AND TECHNOLOGY 19 (4) S409 - S411 0268-1242 2004/04 [Refereed][Not invited]
     
    We have studied the various types of Coulomb interactions in triple quantum dots and estimated their effects on the gate operation of quantum computation. In view of the magnitude of the Coulomb energies, the system requirements for error-free and high-speed operation are discussed.
  • H Sasakura, S Adachi, S Muto, HZ Song, T Miyazawa, T Usuki
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (4B) 2110 - 2113 0021-4922 2004/04 [Refereed][Not invited]
     
    Time-resolved photoluminescence experiments have been performed to investigate exciton spin relaxation processes at low temperatures in InAlAs-InGaAs asymmetric double quantum dots embedded in AlGaAs layers. By decreasing the thickness of the AlGaAs barrier between the dots, the spin relaxation times decreased from 3 ns to 1 ns. The observed spin relaxation as a function of barrier thickness was reasonably described by two components: one was a constant and the other was exponentially depended on barrier thickness. The origin of the latter component is discussed in connection with spin-flip tunneling.
  • H Sasakura, S Adachi, S Muto, HZ Song, T Miyazawa, Y Nakata
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 (2-4) 511 - 515 1386-9477 2004/03 [Refereed][Not invited]
     
    Exciton spin relaxation at low temperatures in InAlAs-InGaAs asymmetric double quantum dots embedded in AlGaAs layers has been investigated as a function of the barrier thickness by the time-resolved photoluminescence measurements. With decreasing the thickness of the AlGaAs layer between the dots, the spin relaxation time change from 3 ns to less than 500 ps. The reduction in the spin relaxation time was considered to originate from the spin-flip tunneling between the ground state in InAlAs dot and the excited states in InGaAs dot, and the resultant tunneling leads to the spin depolarization of the ground state in InGaAs dot. (C) 2003 Elsevier B.V. All rights reserved.
  • S Adachi, H Sasakura, S Muto, K Hazu, T Sota, SK Chichibu, T Mukai
    PHYSICA STATUS SOLIDI B-BASIC RESEARCH 240 (2) 348 - 351 0370-1972 2003/11 [Refereed][Not invited]
     
    Bound and unbound biexcitons in a free-standing, bulk GaN are investigated by time-integrated and spectrally-resolved four-wave mixing measurements, where the formation of hetero-biexcitons that consist of A and B excitons (XXAB) as well as A biexcitons and their unbound biexciton are clearly observed. Through the FWM spectra and delay-time dependence, it is found that the interaction between A and B excitons gives rise to the phase shifts of the quantum beating and the energy shifts of the spectra, which is considered as the effect of the unbound state of XXAB (i.e. XX*(AB)). This interaction is found to play an important role in the FWM signals for all polarizations. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.
  • H Sasakura, S Adachi, S Muto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 42 (10) 6308 - 6313 0021-4922 2003/10 [Refereed][Not invited]
     
    Quantum computation using electron spins in three-coupled dots of different sizes is proposed. By using photon-assisted tunnelling, Coulomb blockade and spin rotation of electrons, logic gates are realized by static and rotational magnetic fields and resonant optical pulses. The two-bit CNOT is numerically demonstrated by the time evolution of the density matrix. In addition, the Hamiltonian is described using pseudo-spin representation and the phase change during the gate operation is discussed.
  • K. Hazu, T. Sota, K. Suzuki, S. Adachi, S. F. Chichibu, G. Cantwell, B. Eason, C. Reynolds, W. Litton
    Physical Review B - Condensed Matter and Materials Physics 68 (11) 1550-235X 2003/07/15 [Refereed][Not invited]
     
    We have studied experimentally biexcitonic states of ZnO of rather high quality in the low exciton density limit by means of time-integrated and spectrally-resolved four-wave mixing (FWM). FWM emission signals due to biexcitons consisting of two A-hole excitons (AA biexcitons), an A-hole and a B-hole exciton (AB biexcitons), and two B-hole excitons (BB biexcitons) have been clearly observed according to polarization selection rules. The obtained binding energies for AA, AB, and BB biexcitons are 15.6, 16.6, and 4.7 meV, respectively. A brief discussion is also given on the contribution of biexciton and two-pair continuum resonances to the FWM signal. © 2003 The American Physical Society.
  • K Hazu, T Sota, K Suzuki, S Adachi, SF Chichibu, G Cantwell, DB Eason, DC Reynolds, CW Litton
    PHYSICAL REVIEW B 68 (3) 033205/1 - 4 2469-9950 2003/07 [Refereed][Not invited]
     
    We have studied experimentally biexcitonic states of ZnO of rather high quality in the low exciton density limit by means of time-integrated and spectrally-resolved four-wave mixing (FWM). FWM emission signals due to biexcitons consisting of two A-hole excitons (AA biexcitons), an A-hole and a B-hole exciton (AB biexcitons), and two B-hole excitons (BB biexcitons) have been clearly observed according to polarization selection rules. The obtained binding energies for AA, AB, and BB biexcitons are 15.6, 16.6, and 4.7 meV, respectively. A brief discussion is also given on the contribution of biexciton and two-pair continuum resonances to the FWM signal.
  • O Ikeuchi, S Adachi, H Sasakura, S Muto
    JOURNAL OF APPLIED PHYSICS 93 (12) 9634 - 9638 0021-8979 2003/06 [Refereed][Not invited]
     
    We observed the exciton spin dynamical processes in GaAs quantum wells at low temperatures by three-pulse spin-diffracted four-wave mixing measurements. After investigating the merits and demerits of this method as compared with the pump-probe method, we discuss the excitation power dependence of exciton spin relaxation and the population transfer to the dark states. (C) 2003 American Institute of Physics.
  • S Adachi, S Muto, K Hazu, T Sota, K Suzuki, SF Chichibu, T Mukai
    PHYSICAL REVIEW B 67 (20) 205212/1 - 5 1098-0121 2003/05 [Refereed][Not invited]
     
    The formation of not only A biexcitons (XXAA) but also heterobiexcitons that consist of A and B excitons (XXAB) in a free-standing bulk GaN is identified by polarization-sensitive spectrally resolved FWM measurements. The FWM spectra and delay-time dependence show that the interaction between A and B exciton gives rise to the energy shifts of the spectra and the phase shifts of the quantum beating, which is considered as the effect of the unbound state of XXAB (i.e., XXAB*) and XXAB* is found to play an important role in the FWM signals for all polarizations. The unbound A biexciton (XXAA*) is also observed clearly in spectral and temporal domains.
  • K Hazu, T Sota, K Suzuki, S Adachi, S Chichibu
    ULTRAFAST PHENOMENA IN SEMICONDUCTORS VII 4992 257 - 264 0277-786X 2003 [Not refereed][Not invited]
     
    Time-integrated and spectrally-resolvd four-wave mixing (FWM) has been used to study dephasing dynamics of excitons in a free-standing bulk ZnO. Clear FWM signals due to AGamma(5)- and BGamma(5)-excitons have been observed. We discuss the dephasing dynamics based on the polariton dispersion and four-particle Coulomb correlations.
  • S Adachi, K Hazu, T Sota, SF Chichibu, T Mukai, S Muto, K Suzuki
    ULTRAFAST PHENOMENA IN SEMICONDUCTORS VII 4992 188 - 201 0277-786X 2003 [Not refereed][Not invited]
     
    Bound and unbound biexcitons in a free-standing bulk GaN are investigated by time-integrated and spectrally-resolved four-wave mixing measurements, where the formation of hetero-biexcitons that consist of A and B excitons (XXAB) as well as A-biexcitons (XXAA) and their unbound biexciton (XXAA*) are clearly observed. The FWM spectra and delay-time dependence are explained qualitatively and the interaction between A- and B-excitons gives rise to the phase shifts of the quantum beating and the energy shifts of the spectra, which is considered as the effect of the unbound state of XXAB (i.e. XXAB*). The unbound A-biexciton (XXAA*) is also observed clearly in spectral and temporal domain and is found to play an important role in FWM signals for all polarizations.
  • S Adachi, S Maki, O Ikeuchi, H Sasakura, S Muto
    ULTRAFAST PHENOMENA IN SEMICONDUCTORS VII 4992 241 - 248 0277-786X 2003 [Refereed][Not invited]
     
    We have observed the exciton spin relaxation processes in GaAs quantum wells at low temperatures by three-pulse spin-diffracted four-wave mixing measurements. After investigating the merits and demerits of this new method as compared with the pump-probe technique, we discuss the population transfer to the dark states through the measurements of the excitation-power dependence of exciton spin relaxation. Spin-diffracted four-wave mixing method is a powerful tool to investigate exciton spin dynamical processes where the pump-probe and time-resolved photoluminescence measurements have been used so far, since the method can be used in reflection geometry and be applicable to thin films and quantum dots.
  • K. Hazu, A. Shikanai, T. Sota, K. Suzuki, S. Adachi, S. F. Chichibu, T. Mukai
    Physical Review B - Condensed Matter and Materials Physics 65 (19) 1952021 - 1952028 0163-1829 2002/05/15 [Refereed][Not invited]
     
    We have studied the properties of coherent exciton states in a free standing wurtzite GaN using the degenerate four-wave-mixing (FWM) technique with subpicosecond time resolution. The polarization dependence of spectrally resolved FWM signals has demonstrated that excitation-induced dephasing is the dominant FWM process. The exciton energy renormalization has been found to dependent on the polarization configuration. FWM signals due to local field effect have been successfully discriminated from those due to other effects. These reveal an importance of four-particle correlations in two-exciton continuum states even for the low excitation power limit where no bound biexciton signal is detected. The temperature dependence of the homogeneous broadening of excitons has also been studied up to 60 K, to obtain the exciton-acoustic phonon interaction coefficient of 9 μeV/K.
  • K Hazu, A Shikanai, T Sota, K Suzuki, S Adachi, SF Chichibu, T Mukai
    PHYSICAL REVIEW B 65 (19) 195202/1 - 8 1098-0121 2002/05 [Refereed][Not invited]
     
    We have studied the properties of coherent exciton states in a free standing wurtzite GaN using the degenerate four-wave-mixing (FWM) technique with subpicosecond time resolution. The polarization dependence of spectrally resolved FWM signals has demonstrated that excitation-induced dephasing is the dominant FWM process. The exciton energy renormalization has been found to dependent on the polarization configuration. FWM signals due to local field effect have been successfully discriminated from those due to other effects. These reveal an importance of four-particle correlations in two-exciton continuum states even for the low excitation power limit where no bound biexciton signal is detected. The temperature dependence of the homogeneous broadening of excitons has also been studied up to 60 K, to obtain the exciton-acoustic phonon interaction coefficient of 9 mueV/K.
  • S Muto, H Sasakura, S Adachi, Y Kajiwara, K Shiramine
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 13 (2-4) 616 - 619 1386-9477 2002/03 [Refereed][Not invited]
     
    Quantum gates using tunneling qubits: tunneling of electrons whose spins work as qubits is described by the Hamiltonian using both electron spins and pseudo-spins representing the photon-assisted tunneling. The phase factor during the controlled-NOT operation is also discussed. Preliminary data on a triple quantum dot system realized by closely stacking technique of molecular beam epitaxy are also shown. (C) 2002 Elsevier Science B.V. All rights reserved.
  • S Adachi, T Tsuchiya, H Mino, S Takeyama, G Karczewski, T Wojitowicz, J Kossut
    PHYSICA E 10 (1-3) 305 - 309 1386-9477 2001/05 [Refereed][Not invited]
     
    Exciton and biexciton optical properties in II-VI semiconductor single quantum well have been studied by magneto-photoluminescence, and time-resolved four-wave-mixing spectroscopies. The polarization dependence of both measurements can clearly distinguish biexciton from other bound states and show the dynamical spin properties of exciton and biexciton. (C) 2001 Elsevier Science B.V. All rights reserved.
  • H Mino, S Takeyama, S Adachi, G Karczewski, T Wojtowicz, J Kossut
    PHYSICA B 298 (1-4) 421 - 425 0921-4526 2001/04 [Refereed][Not invited]
     
    An exciton and a biexciton photoluminescence in (Cd,Mn)Te/CdTe/(Cd,Mg)Te asymmetric quantum wells were investigated under magnetic fields. A quantum beat between an exciton and a biexciton has been observed by a transient four-wave-mixing spectroscopy. The spin-energy structures have been clarified by spectra of the four-wave-mixing signals. We have observed decrease of the intensity ratio of a biexciton to an exciton on increasing magnetic field. The instability of the spin singlet biexciton state is determined by the inner effective magnetic field produced by the local Mn magnetic moments. (C) 2001 Elsevier Science B.V. All rights reserved.
  • S Takeyama, S Adachi, Y Takagi
    PHASE TRANSITIONS 74 (1-2) 175 - 207 0141-1594 2001 [Refereed][Not invited]
     
    Exciton magnetic polarons observed in dilute magnetic semiconductors were investigated by steady-state and pico-second time-resolved photoluminescence measurements and have shown characteristic behavior of exciton localization processes in bulk Cd1-xMnxTe and also in the quantum structures composed of the dilute magnetic semiconductors. For the quantum structures spin-dependent coherent polarizations associated with excitons and biexcitons were studied by degenerate four-wave mixing experiment. Also investigated for different chalcogenide spinel ferromagnetic semiconductors was photo-induced enhancement of exchange interaction between magnetic ions by direct magnetic flux detection in the vicinity of the Curie temperatures.
  • S Takeyama, H Mino, S Adachi, T Stirner, WE Hagston, H Yokoi, YG Semenov, SW Tozer, Y Kim, G Karczewski, J Kossut
    PHYSICA B 294 453 - 458 0921-4526 2001/01 [Refereed][Not invited]
     
    Exciton photoluminescence in a diluted magnetic asymmetric quantum well has given clear evidence of "asymmetric exciton magnetic polaron states" in magnetic fields. The theoretical calculation to interpret the observed magneto-optical data has clarified the importance of exciton localization associated with the interface disorder and the alloy potential fluctuation in addition to the exciton magnetic polaron formation in the asymmetric diluted magnetic barrier. The possibility of a "bifurcated" exciton states is discussed. The transient four-wave-mixing nonlinear spin selective optical measurements revealed the spin-structure of excitons and biexcitons in diluted magnetic quantum structures. The effects of the magnetic field on biexciton states have been investigated. The photoluminescence transition from the biexciton to exciton states has been investigated in magnetic fields, and the stability of the biexciton states in either bonding (spin singlet) or anti-bonding states (spin triplet) is discussed. We have proposed methods to deduce the interface magnetism in the diluted magnetic quantum structures from the high-field Zeeman splitting of exciton photoluminescence up to 60 T. (C) 2001 Elsevier Science B.V. All rights reserved.
  • S. Adachi, S. Muto, K. A. Nelson
    Technical Digest - Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, QELS 2001 208  2001 [Refereed][Not invited]
     
    Summary form only given. In order to investigate the relation between particle diffusion and spin diffusion, we used polarization-dependent transient gratings, an exciton density grating and an exciton spin grating, in optical sampling four-wave mixing measurements (OSFWM), which allows us to measure both particle and spin diffusion in the same system. Because OSFWM has a wide observable temporal range from sub-ps to 13 ns with 200-fs temporal resolution, long recombination is possible to observe, and therefore we can compare directly both diffusions. The sample investigated consists of 25 periods of undoped 68-Å-thick GaAs quantum wells (QWs), alternated with 198-Å-thick Al0.3Ga0.7As barrier layers. The sample was grown on a semi-insulating [100]-GaAs substrate by molecular beam epitaxy.
  • S Adachi, Y Takagi, S Takeyama
    JOURNAL OF CRYSTAL GROWTH 214 819 - 822 0022-0248 2000/06 [Refereed][Not invited]
     
    We have performed two-pulse and three-pulse time-integrated as well as spectrally resolved four-wave-mixing measurements on a single CdMnTe/CdTe/CdMgTe quantum well. The polarization dependence of both four-wave-mixing measurements can be explained well by the five-level model of the exciton-biexciton system including two-biexciton states with parallel spin and anti-parallel spin orientations. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S Adachi, RM Koehl, KA Nelson
    JOURNAL OF LUMINESCENCE 87-9 840 - 843 0022-2313 2000/05 [Refereed][Not invited]
     
    Coherent optic phonon-polaritons generated through impulsive stimulated Raman scattering in a ferroelectric crystal are imaged with 5-mu m spatial resolution and 35-fs time resolution. This imaging spectroscopy allows us to perform direct measurement of space- and time-dependent response function induced by the propagating phonon-polaritons. The method will also permit direct examination of nonlinear lattice dynamics and will provide feedback: in coherent control system. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S. Adachi, Y. Takagi, J. Takeda, K. A. Nelson
    Optics Communications 174 (1-4) 291 - 298 0030-4018 2000/01/15 [Refereed][Not invited]
     
    We have developed the optical sampling four-wave mixing technique applicable to measurements of the ultrafast dynamical processes in liquid and solid materials. The method is examined to reveal the exciton dynamical processes in GaAs quantum wells at low temperatures. By using the optical sampling principle, this new spectroscopic tool provides well timing-controlled two-color light pulses for excitation and detection, and also wide observable temporal range from sub-picoseconds to a few nanoseconds with femtosecond time resolution. Various transient processes such as phase relaxation, spin relaxation, and energy relaxation processes can therefore be observed rapidly in the common measurement system.
  • S Adachi, Y Takagi, J Takeda, KA Nelson
    OPTICS COMMUNICATIONS 174 (1-4) 291 - 298 0030-4018 2000/01 [Refereed][Not invited]
     
    We have developed the optical sampling four-wave mixing technique applicable to measurements of the ultrafast dynamical processes in liquid and solid materials. The method is examined to reveal the exciton dynamical processes in GaAs quantum wells at low temperatures. By using the optical sampling principle, this new spectroscopic tool provides well timing-controlled two-color light pulses for excitation and detection, and also wide observable temporal range from sub-picoseconds to a few nanoseconds with femtosecond time resolution. Various transient processes such as phase relaxation, spin relaxation, and energy relaxation processes can therefore be observed rapidly in the common measurement system. (C) 2000 Elsevier Science B.V. All rights reserved.
  • RM Koehl, S Adachi, KA Nelson
    JOURNAL OF PHYSICAL CHEMISTRY A 103 (49) 10260 - 10267 1089-5639 1999/12 [Refereed][Not invited]
     
    Direct spatiotemporal imaging of optic phonon-polariton wavepackets in polar crystals is demonstrated experimentally and described theoretically. Spatiotemporal imaging permits monitoring of wavepackets as they move through host samples at lightlike speeds. Different imaging methods may be used optimally for wavepackets with different spatial distributions, including spatially periodic or nonperiodic wavepackets. Spatiotemporal imaging holds particular promise for coherent phonon-polariton wavepacket control using spatiotemporal femtosecond pulse shaping.
  • S Takeyama, S Adachi, Y Takagi, G Karczewski, T Wojtowicz, J Kossut, T Karasawa
    MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY 63 (1-2) 111 - 118 0921-5107 1999/08 [Refereed][Not invited]
     
    The temperature dependence of exciton magnetic polaron energies was determined from the pico-second time-resolved photoluminescence (PL) spectra, and have shown characteristic dynamical behavior of exciton localization process in bulk-Cd(1-)xMn(x)Te (x = 0.1-0.2). The overall behavior appears different from that reported previously for the bound- or localized-exciton magnetic polarons (EMP) in the same material. In symmetric diluted magnetic semiconductor (DMS) quantum wells (QWs), CdTe/Cd1-xMnxTe, studied here by steady-state and transient-PL, it is plausible that the exciton magnetic polaron formation occurs after localization by the nonmagnetic disorders. Temperature and magnetic-field dependencies (up to 15 T) of PL have been studied in Cd1-xMnxTe - CdTe-Cd1-yMgyTe asymmetric single QWs. These show the phenomena similar to those expected in the exciton 'bifurcation' effect due to magnetic polaron formation on one side of the diluted magnetic barrier. The doublet PL lines observed are attributed to symmetric and asymmetric exciton states. Biexcitons are observed in DMS-QWs, and confirmed by the polarized two-pulse degenerate four-wave-mixing (DFWM) experiment. (C) 1999 Published by Elsevier Science S.A. All rights reserved.
  • Y Takagi, S Adachi
    REVIEW OF SCIENTIFIC INSTRUMENTS 70 (5) 2218 - 2224 0034-6748 1999/05 [Refereed][Not invited]
     
    We have developed a subpicosecond nondegenerate pump-probe spectrometer based on the optical sampling technique using a combination of asynchronous tunable femtosecond lasers. Owing to its simple instrumentation, time evolution of subpicosecond to nanosecond excited molecular processes in solution and of exciton relaxation processes in semiconductor multiple quantum wells has been detected on an oscilloscope by an effective time base magnification of 760 000 times. Fast acquisition of the temporal profiles and ease of wavelength scanning allowed compilation of time-resolved absorption and excitation spectra. A possible extention of the spectrometer with one of the light sources being a synchrotron radiation instead of the femtosecond laser is discussed. (C) 1999 American Institute of Physics. [S0034-6748(99)03005-1].
  • RM Koehl, S Adachi, KA Nelson
    JOURNAL OF CHEMICAL PHYSICS 110 (3) 1317 - 1320 0021-9606 1999/01 [Refereed][Not invited]
     
    The propagation of collective lattice vibrational wave packets that move at lightlike speeds through their crystalline hosts has been monitored through a real-space imaging method based on Fresnel diffraction and phase-contrast microscopy. Coherent optic phonon-polaritons generated through impulsive stimulated Raman scattering in a ferroelectric crystal are imaged with 5 mu m spatial resolution and 35 fs time resolution as they propagate out of the excitation region and into other parts of the crystal. The "spatiotemporal'' imaging method will permit direct examination of nonlinear lattice dynamics and will provide feedback in coherent control systems that use spatiotemporal femtosecond pulse shaping to manipulate propagating excitations with ultrashort light pulses directed to specified sample locations at specified times. The method will also permit the examination of defects and fabricated structures in bulk or thin film crystals using visible light. (C) 1999 American Institute of Physics. [S0021-9606(99)01803-6].
  • S Adachi, Y Takagi
    PHYSICS OF LOW-DIMENSIONAL STRUCTURES 1-2 133 - 142 0204-3467 1998 [Refereed][Not invited]
     
    We observed the exciton spin dynamical processes in the nonlinear polarization-dependent pump-probe measurements of GaAs/AlGaAs quantum wells and compared the results at low and room temperatures. The results at room temperature clearly indicate that the exciton spin concept is not appropriate and should be analyzed by the separate-particle spin concept. Which concept should be applied depends on the relative importance of the spin exchange interaction to the other spin-flip mechanisms.
  • RM Koehl, S Adachi, KA Nelson
    ULTRAFAST PHENOMENA XI 63 136 - 138 0172-6218 1998 [Refereed][Not invited]
     
    Anharmonic lattice dynamics are investigated with a heterodyne bispectral 2D Raman technique.
  • Y Takagi, S Adachi
    JOURNAL OF LUMINESCENCE 72-4 546 - 547 0022-2313 1997/06 [Refereed][Not invited]
     
    Transient absorption measurement on HDITCI (hexadibenzocyanine-3) dissolved into ethanol was performed by using a dual-wavelength optical sampling method. From time profile data and time-resolved spectra four successive decays ranging from subpicosecond to nanosecond have been found and assigned to intramolecular vibrational diffusion (0.5 ps), solvation relaxation (5 ps), rotational relaxation (160 ps), and radiative decay (0.5 ns).
  • S. Adachi, T. Miyashita, S. Takeyama, Y. Takagi, A. Tackeuchi
    Journal of Luminescence 72-74 307 - 308 0022-2313 1997 [Not refereed][Not invited]
     
    We have investigated the temperature dependence of the exciton spin relaxation between 10 and 300 K in undoped GaAs quantum wells by using the nonlinear transmission pump-probe and the four-wave-mixing techniques. The electron spin relaxation rate above 40 K is found to be proportional to the product of the temperature and the momentum relaxation time, which indicates that the D'yakonov-Perel' interaction governs the spin-flip dynamics. The temperature independence below 30 K is considered to be due to the band-mixing effect that determines the hole spin relaxation, and the spin exchange is effective to the exciton spin relaxation in these temperatures.
  • S Adachi, T Miyashita, S Takeyama, Y Takagi, A Tackeuchi, M Nakayama
    PHYSICAL REVIEW B 55 (3) 1654 - 1660 0163-1829 1997/01 [Refereed][Not invited]
     
    We study the induced absorption due to biexciton formation in absorption bleaching pump-probe signals and the quantum beats between exciton and biexciton in the four-wave-mixing signals. The origin is confirmed by the polarization dependence of the signals in both experiments. The definite discrimination between exciton-biexciton quantum beats and the others by the polarization choices is demonstrated clearly. We also show the well-width dependence of the biexciton binding energy that is determined by the period of the quantum beats in the range of well width 45-150 Angstrom of GaAs/AlxGa1-xAs (x=0.3-1.0) multiple quantum wells.
  • S. Adachi, T. Miyashita, S. Takeyama, Y. Takagi, A. Tackeuchi
    Physical Review B - Condensed Matter and Materials Physics 55 (3) 1654 - 1660 1550-235X 1997 [Refereed][Not invited]
     
    We study the induced absorption due to biexciton formation in absorption bleaching pump-probe signals and the quantum beats between exciton and biexciton in the four-wave-mixing signals. The origin is confirmed by the polarization dependence of the signals in both experiments. The definite discrimination between exciton-biexciton quantum beats and the others by the polarization choices is demonstrated clearly. We also show the well-width dependence of the biexciton binding energy that is determined by the period of the quantum beats in the range of well width 45-150 Å of GaAs/(Formula presented)(Formula presented)As (x=0.3-1.0) multiple quantum wells. © 1997 The American Physical Society.
  • S Adachi, S Takeyama, Y Takagi, A Tackeuchi, S Muto
    APPLIED PHYSICS LETTERS 68 (7) 964 - 966 0003-6951 1996/02 [Refereed][Not invited]
     
    Spin dynamics in GaAs/AlGaAs multiple quantum wells at room temperature are studied in subpicosecond to nanosecond time region by using the optical sampling nondegenerate pump-probe technique. Polarization-dependent absorption signals resonant to the light-hole (lh) exciton revealed the subpicosecond spin relaxation time which was several tens of times shorter than that of the heavy-hole (hh) exciton. Resonant pumping to lh and probing at hh exhibited no spin dependence within the time resolution, showing the spin memory being washed out completely during the energy relaxation from lh to hh. (C) 1996 American Institute of Physics.
  • S Adachi, S Takeyama, Y Takagi, A Tackeuchi, S Muto
    PROGRESS IN CRYSTAL GROWTH AND CHARACTERIZATION OF MATERIALS 33 (1-3) 117 - 120 0146-3535 1996 [Refereed][Not invited]
  • S TAKEYAMA, G GRABECKI, S ADACHI, Y TAKAGI, T WOJTOWICZ, G KARCZEWSKI, J KOSSUT
    ACTA PHYSICA POLONICA A 88 (5) 945 - 948 0587-4246 1995/11 [Refereed][Not invited]
     
    Four-single quantum wells composed of the ternary non-magnetic compounds Cd(0.93)Zn(0.0)7Te (well width = 13, 19, 40, 90 Angstrom), separated by the quaternary magnetic-compound Cd0.48Zn0.04Mn0.48Te on (100)GaAs substrate were grown by MBE, and exhibited clear and distinctive photoluminescence lines corresponding to each quantum well. Double luminescence peaks with closely spaced within one well were observed from 90 Angstrom and 40 Angstrom quantum wells. Temperature and magnetic-field study revealed characteristic luminescence features associated with a bound exciton near the interface rather than with one monolayer fluctuation.
  • G GRABECKI, S TAKEYAMA, S ADACHI, Y TAKAGI, T DIETL, E KAMINSKA, A PIOTROWSKA, E PAPIS, N FRANK, G BAUER
    ACTA PHYSICA POLONICA A 88 (4) 727 - 730 0587-4246 1995/10 [Refereed][Not invited]
     
    Precise magnetoresistance measurements on microstructures of photolithographically patterned PbSe epilayers have been performed in the magnetic field range up to 17 T. Unusually large, reproducible magnetoconductance fluctuations have been observed. The fluctuation amplitude decreases exponentially with the magnetic field. A correlation magnetic field of the fluctuations corresponds to the Aharonov-Bohm effect which involves electron trajectories much smaller than the electron mean free path. This points strongly to the ballistic, not diffusive, origin of the observed phenomenon.
  • G GRABECKI, S TAKEYAMA, S ADACHI, Y TAKAGI, T DIETL, E KAMINSKA, A PIOTROWSKA, E PAPIS, N FRANK, G BAUER
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 34 (8B) 4433 - 4435 0021-4922 1995/08 [Not refereed][Not invited]
     
    Precise magnetoresistance measurements on microstructures of photolithographically patterned PbSe epilayers have been performed in the magnetic field range up to 17 T. Unusual, reproducible magnetoconductance fluctuations have been observed. The fluctuation amplitude is about one order of magnitude greater than that predicted for universal conductance fluctuations. Moreover, the fluctuation frequency spectra correspond to the Aharonov-Bohm effect on electron trajectories up to 50 times smaller than the electron mean free path. This strongly points to the ballistic, not diffusive, origin of the observed phenomenon.
  • S. Takeyama, S. Adachi, Y. Takagi, V. F. Aguekian
    Physical Review B 52 (3) 1444 - 1447 0163-1829 1995/07/15 [Refereed]
  • Satoru Adachi, Shojiro Takeyama, Yoshihiro Takagi
    Optics Communications 117 (1-2) 71 - 77 0030-4018 1995/05 [Refereed]
  • S. Takeyama, S. Adachi, Y. Takagi, V. F. Aguekian
    Physical Review B 51 (8) 4858 - 4864 0163-1829 1995/02/15 [Refereed][Not invited]
  • Y.-W. Chen, C. Yamanaka, H. Niki, S. Adachi, Y. Izawa, S. Nakai
    Journal of the Optical Society of America B 11 (9) 1585 - 1585 0740-3224 1994/09/01 [Refereed]
  • S. Adachi, S. Takeyama, Y. Takagi, J.J. Dubowski, E. Deleporte
    Superlattices and Microstructures 16 (1) 1 - 4 0749-6036 1994/07 [Refereed]
  • G GRABECKI, S TAKEYAMA, S ADACHI, Y TAKAGI, T WOJTOWICZ, G KARCZEWSKI, J KOSSUT
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 34 59 - 61 0021-4922 1994 [Refereed][Not invited]
     
    Exciton photoluminescence has been measured in CdZnTe nonmagnetic single quantum wells surrounded by the magnetic CdZnMnTe barriers. Detailed analysis of the both temperature and magnetic field behaviors of the exciton PL lines points to the conclusion that the contribution from the magnetic polaron and/or magnetization fluctuations to the exciton localization energy is rather small and does not exceed 2 meV even at pumping He temperatures, in the quantum wells as narrow as 1.3 nm.
  • Y. Takagi, S. Adachi, S. Takeyama, A. Tackeuchi, S. Muto, J.J. Dubowski
    Journal of Luminescence 58 (1-6) 202 - 205 0022-2313 1994/01 [Refereed]
  • V.F. Aguekian, S. Takeyama, S. Adachi, Y. Takagi, N. Miura
    Solid State Communications 86 (3) 205 - 208 0038-1098 1993/04 [Refereed]
  • S TAKEYAMA, S ADACHI, Y TAKAGI, VF AGUEKIAN
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 32 425 - 427 0021-4922 1993 [Refereed][Not invited]
     
    The photoluminescence in CdMnTe (with x = 0.15 and 0.35) was carefully studied and clear evidence for the exciton localization due to magnetic polaron (EMP) formation was presented. It was revealed that the EMP localization induced striking features on the luminescence lines; peak positions, FWHM and intensities. The heavy hole and light hole exciton magnetic polaron stability under the magnetic field was demonstrated distinctly by the polarization measurements.
  • S. Takeyama, S. Adachi, Y. Takagi, N. Miura, V.F. Aguekian
    Journal of Crystal Growth 117 (1-4) 1081 - 1081 0022-0248 1992/02 [Refereed]
  • Satoru Adachi, Hideaki Niki, Yasukazu Izawa, Sadao Nakai, Chiyoe Yamanaka
    Japanese Journal of Applied Physics 社団法人応用物理学会 30 (Part 1, No. 10) 2515 - 2518 0021-4922 1991/10/15 [Refereed]
     
    Adiabatic inversion processes are discussed for a two-level system. It was found that the required conditions for stable inversion are $\varOmega^{2}/|\mathrm{d}\varDelta/\mathrm{d}t|{\geq}0.5$, $\varDelta_{\text{s } }\tau{\geq}3$ for Gaussian pulse and $\varDelta_{\text{s } }$/$\varOmega$${\geq}11$ for square pulse, where $\varOmega$, $\varDelta$, $\varDelta_{\text{s } }$ and $\tau$ represent Rabi frequency, detuning, frequency-sweep width and optical pulse width, respectively. It was also shown that for Gaussian pulse, adiabatic conditions of $\varDelta_{\text{s } }$/$\varOmega$ and $\varOmega^{2}/|\mathrm{d}\varDelta/\mathrm{d}t|$ are related to each other, while for square pulse, both conditions are determined independently.
  • Satoru Adachi, Hideaki Niki, Yasukazu Izawa, Sadao Nakai, Chiyoe Yamanaka
    Optics Communications 81 (6) 364 - 368 0030-4018 1991/03 [Refereed]
  • Satoru Adachi, Hideaki Niki, Yasukazu Izawa, Sadao Nakai, Chiyoe Yamanaka
    Japanese Journal of Applied Physics 社団法人応用物理学会 29 (Part 2, No. 5) L833 - L836 0021-4922 1990/05/20 [Refereed]
     
    Dipole matrix elements were measured for two transitions of the gadolinium atom by detecting the laser-induced fluorescence as a function of laser intensity using Rabi flopping. Those values are $2.7\times 10^{-19}$ and $3.0\times 10^{-19}$ esu$\cdot$cm for 9D2-9F2(0-17381 cm-1) and 9D5-9D4(999–17931 cm-1), respectively. Optical Bloch equations for two-level atoms were calculated for each pair of magnetic sublevels, where the effects of inhomogeneous broadening and laser intensity fluctuation were included. Experimental results were well described by this model. This method is very useful for determining a dipole matrix element which is one of the basic parameters for laser isotope separation.
  • Development of a Single-Mode Dye Laser Pumped by a Copper Vapor Laser
    Y. Arai, H. NIki, S. Adachi, T. Takeda, T. Yamanaka, C. Yamanaka
    Technology Reports of the Osaka University 36 (1860) 361 - 367 1986 [Not refereed][Not invited]

Books etc

  • Detection of Coherent Phonons
    ADACHI Satoru (Joint workレーザーハンドブック 26章レーザーによる科学計測 第4節)
    2004

Conference Activities & Talks

  • S. Yasui, T. Inaba, K. Hitachi, A. Ishizawa, R. Kaji, T. Tawara, S. Adachi, X. Xu, H. Sanada
    The 2023 International Conference on Solid State Devices and Materials (SSDM2023)  2023/09
  • S. Adachi, S. Yamamoto, R. Kaji, H. Sasakura
    The 22nd International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON22)  2023/08
  • S. Yasui, T. Inaba, A. Ishizawa, K. Hitachi, H. Omi, R. Kaji, T. Tawara, S. Adachi, X. Xu, H. Sanada
    The 22nd International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON22)  2023/08
  • R. Kaji, S. Yamamoto, Z.-R. Li, H. Sasakura, S. Adachi
    The 22nd International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON22)  2023/08
  • R. Kaji, S. Yamamoto, S. Adachi
    The 2022 International Conference on Solid State Devices and Materials (SSDM2022)  2022/09
  • 安井 翔一郎, 平石 真也, 石澤 淳, 尾身 博雄, 稲葉 智宏, Xuejun Xu, 鍜治 怜奈, 足立 智, 俵 毅彦
    第83回応用物理学会秋季学術講演会  2022/09
  • Remarkable improvement of atomic-frequency-comb memory efficiency by comb transfer method in 167Er3+:Y2SiO5 under zero magnetic field  [Not invited]
    S. Yasui, M. Hiraishi, A. Ishizawa, H. Omi, T. Inaba, X. Xu, R. Kaji, S. Adachi, T. Tawara
    Conference on Lasers and Electro-Optics (CLEO:2022)  2022/05
  • Demonstration of atomic frequency comb time-multiplexed quantum memory protocol in 167Er3+:Y2SiO5 under no magnetic field
    安井翔一郎, 安井翔一郎, 平石真也, 石澤淳, 尾身博雄, 稲葉智宏, XU Xuejun, 鍜治怜奈, 足立智, 俵毅彦
    応用物理学会春季学術講演会講演予稿集(CD-ROM)  2022
  • Frequency and time domain measurements of 167Er3+:Y2SiO5 by stabilizing the optical frequency using a fiber laser comb  [Not invited]
    S. Yasui, M. Hiraishi, A. Ishizawa, H. Omi, R. Kaji, S. Adachi, T. Tawara
    International Symposium on Novel maTerials and quantum Technologies (ISNTT2021)  2021/12
  • 量子情報プラットフォームとしてのEr添加固体材料の開発  [Invited]
    俵 毅彦, 平石 真也, 稲葉 智宏, 徐 学俊, 太田 竜一, 足立 智, 尾身 博雄
    第82回応用物理学会秋季学術講演会  2021/09
  • Evaluation of homogeneous linewidth of 167Er3+:Y2SiO5 in frequency domain measurement using laser stabilization with optical frequency comb  [Not invited]
    S. Yasui, M. Hiraishi, A. Ishizawa, H. Omi, R. Kaji, S. Adachi, T. Tawara
    The 2021 International Conference on Solid State Devices and Materials (SSDM2021)  2021/09
  • Frequency and time domain measurements of dephasing time in Λ type hyperfine sublevel system of 167Er3+:Y2SiO5
    安井翔一郎, 安井翔一郎, 平石真也, 平石真也, 石澤淳, 尾身博雄, 鍜治怜奈, 足立智, 俵毅彦
    応用物理学会春季学術講演会講演予稿集(CD-ROM)  2021
  • Double nuclear spin switching in single self-assembled quantum dots  [Not invited]
    S. Yamamoto, R. Kaji, H. Sasakura, S. Adachi
    The 2020 International Conference on Solid State Devices and Materials (SSDM2020)  2020/09
  • Photon statics in a single quantum dot under bistable state of nuclear spin polarization  [Not invited]
    R. Kaji, R. Matsusaki, K. Omiya, S. Kamono, H. Sasakura, S. Adachi
    International Conference on Optics of Excitons in Confined Systems  2019/09
  • Large in-plane nuclear field formation in single quantum dots: Influence of a longitudinal field and role of nuclear quadrupolar interaction  [Not invited]
    S. Yamamoto, T. Arakawa, R. Matsusaki, R. Kaji, S. Adachi
    International Conference on Optics of Excitons in Confined Systems  2019/09
  • Generation of in-plane nuclear field orthogonal to injected electron spin in single quantum dots  [Invited]
    S. Adachi, S. Yamamoto, T. Arakawa, R. Kaji
    日本物理学会2019年秋季大会  2019/09
  • Modulation of nuclear quadrupole effect by a longitudinal magnetic field in transverse nuclear field formation  [Not invited]
    S. Yamamoto, T. Arakawa, R. Matsusaki, R. Kaji, S. Adachi
    The 46th International Symposium on Compound Semiconductors  2019/05
  • Evaluation of Rabi frequency and coherence time in the hyperfine structure of 167Er3+ in Y2SiO5 through coherent transients  [Not invited]
    M. Hiraishi, M. IJspeert, T. Tawara, S. Adachi, H. Omi, H. Gotoh
    The 46th International Symposium on Compound Semiconductors  2019/05
  • Nuclear spin switching in a single quantum dot  [Invited]
    S. Adachi
    The 3rd Japan-Taiwan International Engineering Forum  2019/02
  • Studies on anomalous Hanle effect observed in single self-assembled quantum dots  [Not invited]
    R. Kaji, S. Yamamoto, R. Matsusaki, S Adachi
    The 50th International Conference on Solid State Devices and Materials: SSDM2018  2018/09
  • A novel method for direct evaluation of nuclear spin fluctuation by using nuclear spin switch in quantum nanostructures  [Not invited]
    R. Kaji, R. Matsusaki, S. Yamamoto, S Adachi
    The 50th International Conference on Solid State Devices and Materials: SSDM2018  2018/09
  • Anomalous Hanle curves induced by in-plane nuclear field in single self-assembled InAlAs and InAs nanostructures  [Not invited]
    S. Yamamoto, R. Matsusaki, R. Kaji, S Adachi
    The 12th International Conference on Excitonic and Photonic Processes in Condensed Matter and Nano Materials: EXCON2018  2018/07
  • Formation of nuclear field orthogonal to electron spin and nuclear quadrupole effects in self-assembled single quantum dots  [Not invited]
    S. Yamamoto, R. Matsusaki, R. Kaji, S Adachi
    50 years of optical orientation in semiconductors: From the original discovery to new horizons  2018/06
  • State preparation and lifetime measurements through spectral hole burning in 167Er3+:Y2SiO5  [Not invited]
    M. IJspeert, M. Hiraishi, T. Tawara, K. Shimizu, H. Omi, S. Adachi, H. Gotoh
    International School and Symposium on Nanoscale Transport and phoTonics (ISNTT2017)  2017/11
  • n-plane nuclear field formation in individual InAlAs quantum dots: role of nuclear quadrupole effects  [Not invited]
    S. Yamamoto, R. Matsusaki, R. Kaji, S Adachi
    International School and Symposium on Nanoscale Transport and phoTonics (ISNTT2017)  2017/11
  • Evaluations of the electron g-factor anisotropy and fuctuationof the Overhauser field in single quantum dots  [Not invited]
    R. Matsusaki, S. Yamamoto, R. Kaji, S Adachi
    International School and Symposium on Nanoscale Transport and phoTonics (ISNTT2017)  2017/11
  • Formation of transverse nuclear field in single self-assembled quantum dots: role of quadrupolar splitting  [Invited]
    S Adachi
    International Workshop on NanoScience and NanoOptics  2017/11
  • Population trapping through spectral hole burning in 167Er3+:Y2SiO5  [Not invited]
    M. IJspeert, G. Mariani, T. Tawara, K. Shimizu, H. Omi, S. Adachi, H. Gotoh
    International Conference on Solid-State Devices and Materials (SSDM2017)  2017/09
  • Λ-system Initialisation through Spectral Hole Burning in 167Er3+:Y2SiO5  [Not invited]
    M. IJspeert, G. Mariani, T. Tawara, K. Shimizu, H. Omi, S. Adachi, H. Gotoh
    International Symposium on Hybrid Quantum Systems 2017 (HSQ2017)  2017/09
  • Quadrupolar effect for nuclear spin depolarization in a single InAlAs quantum dot  [Not invited]
    R. Kaji, R. Matsusaki, S. Yamamoto, H. Sasakura, S. Adachi
    International Conference on Optics of Excitons in Confined Systems (OECS2017)  2017/09
  • Formation mechanism of in-plane Overhauser field in single self-assembled InAlAs quantum dots  [Not invited]
    S. Yamamoto, R. Matsusaki, R. Kaji, S Adachi
    International Conference on Optics of Excitons in Confined Systems (OECS2017)  2017/09
  • Quadrupolar effect in zero-field dynamic nuclear spin polarization of a single self-assembled InAlAs quantum dot  [Not invited]
    R. Matsusaki, S. Yamamoto, R. Kaji, S. Adachi
    The 9th International Conference on Spintronics and Quantum Information Technology  2017/06
  • Spectral Hole Narrowing in Er3+ 4f Transitions by Isotope Separation  [Not invited]
    T. Tawara, G. Mariani, K. Shimizu, H. Omi, S. Adachi, H. Gotoh
    Conference on Lasers and Electro-Optics (CLEO2017)  2017/05
  • 俵 毅彦, Mariani Giacomo, 清水 薫, 尾身 博雄, 足立 智, 後藤 秀樹
    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  2017/01  電子情報通信学会
  • Investigation of Spin Dynamics Based on Initial Phase Shift Analysis of Kerr Rotation in a CdTe Single Quantum Well  [Not invited]
    L.-P. Yan, R. Kaji, S. Adachi
    The 43rd International Symposium on Compound Semiconductors (ISCS)  2016/06
  • Hole g-Factor Anisotropies in Individual InAs Quantum Rings  [Not invited]
    R. Kaji, T. Tominaga, Y.-N. Wu, M.-F. Wu, S.-J. Cheng, S. Adachi
    The 43rd International Symposium on Compound Semiconductors (ISCS)  2016/06
  • Photonic crystal membrane with single crystalline rare-earth oxide using selective area growth by MBE  [Not invited]
    T. Tawara, H. Omi, T. McManus, A. Llenas, E. Kuramochi, S. Adachi, H. Gotoh
    The 43rd International Symposium on Compound Semiconductors (ISCS)  2016/06
  • Control of energy transfer up-conversion by photonic band gap in Er2O3 epitaxial layers  [Not invited]
    T. Tawara, A. Llenas, T. McManus, H. Omi, E. Kuramochi, S. Adachi, H. Gotoh
    International Symposium on Nanoscale Transport and Technology (ISNTT2015)  2015/11
  • Anisotropy of electron and hole in-plane g-factors in single InAs/GaAs quantum rings  [Not invited]
    T. Tominaga, R. Kaji, Y.-N. Wu, S.-J. Cheng, S Adachi
    17th International Conference on Modulated Semiconductor Structures (MSS17)  2015/07
  • Anisotropy of electron and hole g-factors in individual InAs quantum rings  [Invited]
    R. Kaji, S. Adachi
    Japan, Vietnam, Bulgaria and Taiwan Joint Workshop  2015/07
  • Inter- and intra-site energy transfers in (Er, Sc)2O3 thin films grown on Si(111)  [Not invited]
    Y. Kawakami, T. Tawara, H. Omi, R. Kaji, S. Adachi
    19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 19)  2015/07
  • Electron and hole in-plane g-factors in single InAs quantum rings  [Not invited]
    R. Kaji, T. Tominaga, Y.-N. Wu, S.-J. Cheng, S. Adachi
    19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 19)  2015/07
  • Formation dynamics and initial phase shift of resident electron spin polarization observed by time-resolved Kerr rotation spectroscopy  [Not invited]
    L.-P.Yan, R. Kaji, S. Adachi
    17th International Conference on Modulated Semiconductor Structures (MSS17)  2015/06
  • Visible up-conversion luminescence in (ErSc)2O3 epitaxial thin films and its suppression by photonic band-gap  [Not invited]
    T. Tawara, T. McManus, Y. Kawakami, H. Omi, A. Najar, R. Kaji, S. Adachi, H. Gotoh
    onference on Lasers and Electro-Optics (CLEO:2015)  2015/05
  • Electron and hole spin dephasing induced by nuclear field fluctuation in semiconductor quantum dots  [Invited]
    R. Kaji, S. Adachi
    International Symposium on Recent Progress of Photonic Devices and Materials  2014/11
  • Effective nuclear field measurement in a single quantum well via time-resolved Kerr rotation technique  [Not invited]
    L.-P. Yan, R. Kaji, S. Adachi
    International Conference on Materials Science and Engineering Technology (MSET 2014)  2014/06
  • Optical transition between Stark levels in (ErSc)2O3 epitaxitial films  [Not invited]
    T. Tawara, H. Omi, A. Najar, R. Kaji, S. Adachi, H. Gotoh
    Conference on Lasers and Electro-Optics (CLEO:2014)  2014/06
  • Molecular beam epitaxy of (ErxSc1-x)2O3 in Si(111)  [Not invited]
    H. Omi, T. Tawara, T. Hozumi, R. Kaji, S. Adachi, H. Gotoh, T. Sogawa
    2nd International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2014)  2014/01
  • Resident electrons spin formation and spin dephasing in a single CdTe quantum well  [Not invited]
    L.-P. Yan, W.-T.Hsu, S. Adachi
    International Conference on Solid State Devices and Materials (SSDM13)  2013/09
  • MBE growth and optical properties of rear earth oxides on Si(111)  [Not invited]
    H.Omi, T. Tawara, T. Hozumi, R. Kaji, T. Adachi, H. Gotoh, T. Sougawa
    2013 JSAP-MRS Joint Symposia  2013/09
  • Magneto-optical properties of Er2O3 epilayers on Si(111)  [Not invited]
    T. Hozumi, R. Kaji, S. Adachi, T. Tawara, H. Omi
    2013 JSAP-MRS Joint Symposia  2013/09
  • Energy transfer in epitaxial Er2O3 thin films grown on Si(111) substrates  [Not invited]
    T. Tawara, T. Hozumi, H. Omi, R. Kaji, S. Adachi, H. Gotoh, T. Sogawa
    IEEE Photonics Conference 2013  2013/09
  • Coherent dynamics of excitons in Wide-gap semiconductors under intense excitation conditions
    Hasegawa A., Toda Y., Adachi S., Morita R., Nakayama M.
    Meeting abstracts of the Physical Society of Japan  2013/08  The Physical Society of Japan (JPS)
  • Electron and hole g-factor measurements via optically-induced nuclear spin polarizations in single InAs/GaAs quantum rings  [Not invited]
    R. Kaji, T. Hozumi, S. Ohno, S. Adachi
    13th International Conference on Optics of Excitons in Confined System: OECS13  2013/08
  • Impact of band mixing to heavy hole spin dephasing induced by nuclear field fluctuation  [Not invited]
    R. Kaji, S. Ohno, T. Hozumi, S. Adachi
    18th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures: EDISON18  2013/07
  • Arbitrary qubit rotation by double STIRAP in Er2O3 thin film  [Not invited]
    Y. Kawakami, T. Hozumi, R. Kaji, S. Adachi, T. Tawara, H. Omi
    18th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures: EDISON18  2013/07
  • 26pXG-6 Optical pumping of nuclear spin polarization and detection of its fluctuation in single self-assembled quantum dots
    Kaji Reina, Adachi Satoru
    Meeting abstracts of the Physical Society of Japan  2013/03  The Physical Society of Japan (JPS)
  • 強励起条件下におけるワイドギャップ半導体励起子の縮退四光波混合
    長谷川明, 戸田泰則, 足立智, 森田隆二, 中山正昭
    応用物理学会北海道支部・日本光学会北海道地区合同学術講演会講演予稿集  2013
  • Exciton-exciton interactions in tensile-strained GaN  [Not invited]
    Y. Toda, K. Shigematsu, A. Hasegawa, S. Adachi
    International Workshop on NItride Semiconductors:IWN2012  2012/10
  • Size distribution and scaling function of InAlAs/AlGaAs quantum dots grown on GaAs by molecular beam epitaxy  [Not invited]
    X. M. Lu, M. Koyama, Y. Izumi, S. Adachi, S. Muto
    7th International Conference on MBE:MBE2012  2012/09
  • Spin interactions of electron and nuclei in individual quantum dots  [Invited]
    S. Adachi
    Workshop on“Fabrication, Spectroscopy and Modeling of Semiconductor Quantum Dots  2012/03
  • 四光波混合を用いた光の軌道角運動量の変換
    上野雄鋭, 戸田泰則, 足立智, 森田隆二, 俵毅彦
    応用物理学会学術講演会講演予稿集  2009
  • InAs/GaAs量子リングにおける励起子微細構造分裂の抑制
    定昌史, SURAPRAPAPICH S., TU C.W., 林雄二郎, 笹倉弘理, 熊野英和, 末宗幾夫, 末宗幾夫, 足立智, 足立智, 武藤俊一, 武藤俊一
    応用物理学関係連合講演会講演予稿集  2008
  • 四光波混合分光によるGaN励起子のトポロジカル解析
    上野雄鋭, 上野雄鋭, 戸田泰則, 戸田泰則, 足立智, 森田隆二, 俵毅彦
    応用物理学会学術講演会講演予稿集  2008
  • 24aPS-42 Four wave mixing spectroscopy of GaN films on A-plane sapphire
    Toda Y., Adachi S., Abe Y., Hoshino K., Arakawa Y.
    Meeting abstracts of the Physical Society of Japan  2005/03  The Physical Society of Japan (JPS)
  • 綿貫丈雄, 足立 智, 笹倉弘理, 武藤俊一, 宋 海智, 竹本一矢, 臼杵達哉
    応用物理学会  2005/03
  • Watanuki T, Adachi S, Sasakura H, Muto S, Tsujimi Y, Yagi T, Song H.Z, Takemoto K, Usuki T
    Meeting abstracts of the Physical Society of Japan  2004/03  The Physical Society of Japan (JPS)
  • 30aPS-24 Selective excitation of biexcitons in ZnO by controlled two-photon coherence
    Adachi S., Hazu K., Sota T., Suzuki K., Chichibu S. F.
    Meeting abstracts of the Physical Society of Japan  2004/03  The Physical Society of Japan (JPS)
  • 28pXQ-3 Four-wave mixing signals at C-exciton rcsonances in ZnO
    Hazu K., Sota T., Adachi S., Chichibu SF.
    Meeting abstracts of the Physical Society of Japan  2004/03  The Physical Society of Japan (JPS)
  • Watanuki T, Umemura Y, Adachi S, Sasakura H, Tsujimi Y, Yagi T, Mutoh S
    Meeting abstracts of the Physical Society of Japan  2003/08  The Physical Society of Japan (JPS)
  • Temperature dependence of four-wave mixing signals in ZnO
    Hazu K., Sota T., Suzuki K., Adachi S., Chichibu SF.
    Meeting abstracts of the Physical Society of Japan  2003/08  The Physical Society of Japan (JPS)
  • Valence-band ordering in ZnO
    Hazu K., Torii K., Sota T., Suzuki K., Adachi S., Chichibu SF.
    Meeting abstracts of the Physical Society of Japan  2003/03  The Physical Society of Japan (JPS)
  • FWM measurements of exciton-exciton correlation in ZnO
    Adachi S., Hazu K., Sota T., Suzuki K., Chichibu SF.
    Meeting abstracts of the Physical Society of Japan  2003/03  The Physical Society of Japan (JPS)
  • Optical nonlinearities of excitons in GaN using pump and probe spectroscopy
    Hazu K., Sota T., Suzuki K., Adachi S., Chichibu S., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2002/08  The Physical Society of Japan (JPS)
  • Exciton and Biexciton Behavior Investigated by Four-wave-mixing in High Magnetic Fields II
    Kobayashi A., Mino H., Takeyama S., Adachi S.
    Meeting abstracts of the Physical Society of Japan  2002/08  The Physical Society of Japan (JPS)
  • Dephasing dynamics in exciton-biexciton system of GaN
    Adachi S., Hazu K., Sota T., Suzuki K., Chichibu S., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2002/08  The Physical Society of Japan (JPS)
  • 24aYE-8 Optical nonlinearities of excitons in GaN using pump and probe methods
    Hazu K., Sota T., Suzuki K., Adachi S., Chichibu S. F., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2002/03  The Physical Society of Japan (JPS)
  • 24pYE-4 Biexciton States of II-VI Semiconductor Quantum Wells
    Mino H., Takeyama S., Adachi A S., Akimoto R.
    Meeting abstracts of the Physical Society of Japan  2002/03  The Physical Society of Japan (JPS)
  • Quantum computing using electron spins in a quantum-dot-chain
    Sasakura H., Adachi S., Shiramine K., Muto S.
    Meeting abstracts of the Physical Society of Japan  2001/09  The Physical Society of Japan (JPS)
  • Biexciton Spin States of Diluted Magnetic Semiconductor Quantum Wells in High Magnetic Fields III
    Mino H., Takeyama S., Adachi S.
    Meeting abstracts of the Physical Society of Japan  2001/09  The Physical Society of Japan (JPS)
  • Interaction and dephasing of excitons in GaN
    Hazu K., Sota T., Suzuki K., Adachi S., Chichibu S. F., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2001/09  The Physical Society of Japan (JPS)
  • Exciton-exciton interaction and biexciton formation in GaN eplayers
    Adachi S., Hazu K., Sota T., Suzuki K., Chichibu S. F., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2001/09  The Physical Society of Japan (JPS)
  • Biexciton Spin States of Diluted Magnetic Semiconductor Quantum Wells in High Magnetic Fields II
    Mino H., Hamada S., Takeyama S., Adachi S.
    Meeting abstracts of the Physical Society of Japan  2001/03  The Physical Society of Japan (JPS)
  • Dephasing dynamics in GaN eplayers
    Adachi S., Shikanai A., Hazu K., Sota T., Chichibu S. F., Mukai T.
    Meeting abstracts of the Physical Society of Japan  2001/03  The Physical Society of Japan (JPS)
  • Possible biexciton transition observed by optical reflection spectra in CdTe/CdMnTe single quantum well  [Not invited]
    H Mino, S Hamada, S Takeyama, S Adachi, G Karczewski, T Wojtowicz, J Kossut
    PROCEEDINGS OF THE 10TH INTERNATIONAL CONFERENCE ON NARROW GAP SEMICONDUCTORS AND RELATED SMALL ENERGY PHENOMENA, PHYSICS AND APPLICATIONS  2001  INST PURE APPLIED PHYSICS
     
    We report on a study of the exciton transition in CdTe/CdMnTe quantum well by magneto-optical measurements. A distinct spectral structure at lower energy side of the exciton state has been observed both in photoluminescence and reflection measurements. This structure is explained well by the biexciton transition model. The photoluminescence intensity of this structure tends to remain under high magnetic field, of which feature is inconsistent with possible charged exciton transition.
  • Real-space and real-time imaging of phonon wavepackets II
    Adachi S., Kohel Richard M., Nelson Keith A.
    Meeting abstracts of the Physical Society of Japan  2000/09  The Physical Society of Japan (JPS)
  • Biexciton Spin State of Diluted Magnetic Semiconductor Quantum Wells in High Magnetic Field
    Mino H., Hamada S., Takeyama S., Adachi S.
    Meeting abstracts of the Physical Society of Japan  2000/09  The Physical Society of Japan (JPS)
  • Photoinduced magnetization in Chalcogenide Spinel ferro-magnetic semiconductors in the vicinty of Tc
    Miura M., Adachi S., Aguekian V. F., Takagi Y.
    Meeting abstracts of the Physical Society of Japan  2000/03  The Physical Society of Japan (JPS)
  • Study of surface magnetic properties by nonlinear magnetic Kerr effect : Setup and performance of observation system
    Kawaguchi Y., Adachi S., Takagi Y.
    Meeting abstracts of the Physical Society of Japan  2000/03  The Physical Society of Japan (JPS)
  • Acousto-optic pulse shaping of femtosecond laser pulses II
    Serada K., Inagaki K., Adachi S., Takagi Y.
    Meeting abstracts of the Physical Society of Japan  2000/03  The Physical Society of Japan (JPS)
  • 高強度フェムト秒波長可変光源の開発 (大阪大学レーザー核融合研究センターS)
    石坂隆典, 足立智, 高木芳弘, 佐藤文信, 阪部周二, 井沢靖和
    大阪大学レーザー核融合研究センター共同研究成果報告書  2000
  • 29a-ZE-13 Bi-Excitons in Dilute Magnetic Semiconductor Quantum Structures
    Takeyama S., Karczewski G., Wojtowicz T., Kossut J.
    Meeting abstracts of the Physical Society of Japan  1999/03  The Physical Society of Japan (JPS)
  • 28p-ZG-12 Photoinduced magnetization in magnetic semiconductor HgCr_2Se_4 in the vicinty of Tc
    Miura M., Adachi S., Aguekian V.E., Takagi Y.
    Meeting abstracts of the Physical Society of Japan  1999/03  The Physical Society of Japan (JPS)
  • 28p-ZE-3 Development and application of ultrafast optical sampling four-wave-mixing spectroscopy
    Adachi S., Takagi Y., Takeda J.
    Meeting abstracts of the Physical Society of Japan  1999/03  The Physical Society of Japan (JPS)
  • 28p-ZE-4 AO pulse shaping of femtosecond laser pulses
    Serada K., Adachi S., Takagi Y.
    Meeting abstracts of the Physical Society of Japan  1999/03  The Physical Society of Japan (JPS)
  • 石坂隆典, 足立智, 高木芳弘, 川戸栄, 阪部周二, 井沢靖和
    大阪大学レーザー核融合研究センター共同研究成果報告書  1999/03
  • Studies on exciton relaxation process in (Cd,Mn)Te/CdTe/(Cd,Mg)Te single quantum well I
    ADACHI S., TAKEYAMA S., TAKAGI Y., KARCZEWSKI G., WOJTOWICZ T., KOSSUT J.
    Meeting abstracts of the Physical Society of Japan  1998/09  The Physical Society of Japan (JPS)
  • Real-Space Imaging of Phonon-Polaritons
    ADACHI Satoru, KOEHL Richard M, NELSON Kelth A
    Meeting abstracts of the Physical Society of Japan  1998/09  The Physical Society of Japan (JPS)
  • Photoinduced magnetization in spinel magnetic semiconductors-II : Excitation energy and excitation power dependences
    MIURA M., ADACHI S., TAKEYAMA S., TAKAGI Y., AGUEKIAN V.F
    Meeting abstracts of the Physical Society of Japan  1998/09  The Physical Society of Japan (JPS)
  • Spatial bifurcation and magnetoluminescence of exciton magnetic polarons in diluted magnetic semiconductor asymmetric quantum wells.
    TAKEYAMA S., KARCZEWSKI G., WOJTOWICZ T., KOSSUT J.
    Meeting abstracts of the Physical Society of Japan  1998/09  The Physical Society of Japan (JPS)
  • The effect of photoinduced enhancement of magnetization in magnetic semiconductor CdCr_2S_4 single crystal In the vicinity of Curie point
    YOKOTANI H., MIURA M., ADACHI S., TAKEYAMA S., TAKAGI Y., AGUEKIAN V.F.
    Meeting abstracts of the Physical Society of Japan  1998/03  The Physical Society of Japan (JPS)
  • Two-Color Impact Excitation of Heavy-Hole Exciton and Light-Hole Exciton in a GaAs/AlGaAs Superlattice
    TAKAGI Y., IHARA A., ADACHI S.
    Meeting abstracts of the Physical Society of Japan  1998/03  The Physical Society of Japan (JPS)
  • Two dimensional imaging of propagating phonon-polariton in LiTaO_3
    ADACHI Satoru, KOEHL Richard M, NELSON Keith A.
    Meeting abstracts of the Physical Society of Japan  1998/03  The Physical Society of Japan (JPS)
  • 29p-R-11 Exciton Free Magnetic Polarons in CdTe/Cd_<1-x>Mn_xTe SQWs II
    Najima N, Takeyama S, Adachi S, Takagi Y, Wojtowicz T, Krczewski G, Kossut J
    Meeting abstracts of the Physical Society of Japan  1997/03  The Physical Society of Japan (JPS)
  • Development of asynchronous femtosecond pump-probe spectroscopy
    TAKAGI Y., ADACHI S.
    レーザー学会学術講演会年次大会講演予稿集 = Annual meeting, of the Laser Society of Japan digest of technical papers  1997/01
  • 高木 芳弘, 足立 智, 岳山 正二郎
    レーザー研シンポジウム共同研究成果報告書  1996/11  大阪大学レーザー核融合研究センター
  • Observation of biexciton binding energy by DFWM
    Miyashita T., Adachi S., Takeyama S., Takagi Y., Nakayama Masaaki
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1996/09  The Physical Society of Japan (JPS)
  • Exciton Spin Relaxation Mechanisms in GaAs Quantum Wells II
    Adachi Satoru, Takeyama Shojiro, Takagi Yoshihiro, Nakayama Masaaki, Takeuchi Atsushi
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1996/09  The Physical Society of Japan (JPS)
  • Non-Degenerate Pump-Probe Spectroscopy by Femotosecond-Pulse Phase modulation
    Takagi Yoshihiro, Adachi Satoru
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1996/09  The Physical Society of Japan (JPS)
  • Photoinduced magnetic domain oscillation in CdCr_2Se_4 single crystal
    Takagi Yoshihiro, Yokotani Hirotugu, Adachi Satoru, Takeyama Syojiro, Aguekian V.F.
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1996/09  The Physical Society of Japan (JPS)
  • 3a-X-4 Exciton Spin Relaxation Mechanism in GaAs Quantum Wells
    Adachi Satoru, Miyashita Takeshi, Takeyama Shojiro, Takagi Yoshihiro
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1996/03  The Physical Society of Japan (JPS)
  • 2p-X-11 Photoinduced magnetism in CdCr_2Se_4 single crystal II
    Takagi Yoshihiro, Yokotani Hirotugu, Adachi Satoru, Takeyama Syojiro, Aguekian V.F.
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1996/03  The Physical Society of Japan (JPS)
  • 2p-X-6 Free Exciton Magnetic Polarons in CdTe/Cd_<1-x>Mn_xTe SQW's
    Najima N., Takeyama S., Adachi S., Takagi Y., Wojtowicz T., Karczewski G., Kossut J.
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1996/03  The Physical Society of Japan (JPS)
  • 31p-Y-6 Exciton relaxation in CdTe thin film
    Miyashita T, Adachi S, Takeyama S, Takagi Y
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1996/03  The Physical Society of Japan (JPS)
  • 30a-Z-5 2D Exciton Magnetic Polaron Localization in CdTe/Cd_<1-x>Mn_xTe Superlattices
    Najima N., Takeyama S., Adachi S., Takagi Y., Dubowski J.J., Wojtowicz T., Karczewski G., Kossut J.
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1995/09  The Physical Society of Japan (JPS)
  • 30a-Z-10 Photoinduced magnetism in CdCr_2Se_4 single crystal II
    Adachi Satoru, Yokotani Hirotugu, Takeyama Syojiro, Takagi Yoshihiro, Aguekian V.F.
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1995/09  The Physical Society of Japan (JPS)
  • The measurements of exciton relaxation in GaAs/AlGaAs MQW by sampling pump-probe technique
    Adachi S, Takahashi N, Takeyama S, Takagi Y
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1995/03  The Physical Society of Japan (JPS)
  • Photoinduced magnetism in CdCr_2Se_4 single crystal
    Murata Kazuho, Takagi Yoshihiro, Takeyama Syojiro, Adachi Satoru, Aguekian V.F
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1995/03  The Physical Society of Japan (JPS)
  • 2D Exciton Magnetic Poralon Localization in CdTe/Cd_<1-x>Mn_xTe Superlattice
    Najima N, Takeyama S, Adachi S, Takagi Y, Dubowski J.J
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1995/03  The Physical Society of Japan (JPS)
  • Exciton Magneto-photoluminescence in New Diluted Magnetic Semiconductor Super-Structures CdZnTe/CdZnMnTe
    Takeyama S, Grabecki G, Adachi S, Takagi Y, Wojtowicz T, Karczewski G, Kossut J
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1995/03  The Physical Society of Japan (JPS)
  • 非縮退ポンプ・プローブ分光のための超高速サンプリング法
    足立 智, 嶽山 正二郎, 高木 芳弘
    レーザー学会学術講演会年次大会講演予稿集 = Annual meeting, of the Laser Society of Japan digest of technical papers  1995/01
  • 4a-G-6 Two color ultrafast spectroscopy using the independently tunable lasers
    Adachi S, Takahashi N, Takeyama S, Takagi Y
    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1994/08  The Physical Society of Japan (JPS)
  • 31a-H-6 Relaxation dynamics of excitions in a CdTe-CdMnTe multiple quantum well III
    Adachi Satoru, Takeyama Shojiro, Takagi Yoshihiro, Dubowski J.J
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1994/03  The Physical Society of Japan (JPS)
  • 31a-H-5 Novel method for non frequency-degenerated ultrafast pump-probe spectroscopyII
    Adachi Satoru, Takeyama Syojiro, Takagi Yoshihiro
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1994/03  The Physical Society of Japan (JPS)
  • 28a-K-9 Free Exciton Magnetic Polaron Localization in Semimagnetic Semiconductors Observed by Polarized Magneto-Photoluminescence
    Takeyama S, Adachi S, Takagi Y, Aguekian V.F
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1994/03  The Physical Society of Japan (JPS)
  • Excition localizations and their dynamics in Semimagnetic Semiconductors observed by a weak excitation photoluminescence.
    岳山正二郎, 足立智, 高木芳弘, 唐沢力, 赤井一郎, 小松晃雄, AGUEKIAN V F
    日本物理学会講演概要集(分科会)  1994
  • 30a-N-12 Magnetic field induced photoluminescence in Semimagnetic Semiconductors and its polarization dependences - at a low feild region
    Takeyama S., Adachi S., Takagi Y., Aguekian V.F.
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1993/03  The Physical Society of Japan (JPS)
  • 1p-N-13 Spin relaxation of excitons in CdTe/CdMnTe quantum wells
    Adachi S., Takeyama S., Takagi Y., Dubouski J.J.
    Abstracts of the meeting of the Physical Society of Japan. Annual meeting  1993/03  The Physical Society of Japan (JPS)
  • 28p-ZH-2 Spin relaxation of excitons in GaAs/AlGaAs quantum wells
    Adachi S, Takeyama S, Takagi Y, Takeuchi A, Muto S
    秋の分科会講演予稿集  1992/09  The Physical Society of Japan (JPS)
  • 28p-F-10 Magneto-optical properties of CdTe-CdMnTe multiple quantum well structures
    Takeyama S, Adachi S, Takagi Y, Miura N, Dubowski J.J
    年会講演予稿集  1992/03  The Physical Society of Japan (JPS)
  • 27p-C-5 Magnetic Field Induced Luminescence of Exciton in Semimagnetic Semiconductor CdMnTe
    Takeyama S., Adachi S., Takagi Y., Miura N., Aguekian V.F.
    年会講演予稿集  1991/09  The Physical Society of Japan (JPS)

MISC

Industrial Property Rights

  • 特開USSN 60/092,429:Polariton Wave Imaging  
    ADACHI Satoru  Keith A. Nelson, Satoru Adachi, Richard M. Koehl
  • 位相干渉計測手法及び位相干渉計測装置
    2006-128277
  • 「光計測評価方法および光計測評価装置」（世界知的所有権）
    PCT/JP2005/020410
  • 光計測評価方法及び光計測評価装置
    2004-331123

Research Grants & Projects

  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2023/06 -2025/03 
    Author : 足立 智
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2022/04 -2025/03 
    Author : 俵 毅彦, 足立 智, 尾身 博雄, 徐 学俊, 稲葉 智宏
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2021/04 -2024/03 
    Author : 足立 智, 鍜治 怜奈, 笹倉 弘理
     
    単一量子ドットに適用可能なＮＭＲ測定系の構築，電子－核スピン結合系の数値シミュレーション，核スピン分極の三重安定状態の実験的調査を行った．ＮＭＲ測定で核四極子相互作用について直接的に調べるため，試料に効率よくRF磁場を照射するための電気回路が必要であった．簡易な遺伝的アルゴリズムでは回路が最適化できなかったため，整合を取らずに高周波アンプでRF磁場を増幅する手法を選択した．現在は，複数の任意波形発生器を用いた測定シーケンスの実装を行っている．数値シミュレーションでは，異常ハンル効果が発現する条件を探るため，核四極子相互作用の主軸分布に着目した計算を実装した．計算から，結晶成長方向から大きくずれた主軸や相互作用の二軸性が異常ハンル効果の発現に必要であるという画期的な結果を得た．また異常ハンル効果の時間分解測定を行い，従来モデルでは説明できない結果を得てモデルを再考し，横磁場および縦磁場配置でこれまでに得た時間分解・定常発光測定データの両方を矛盾なく説明できる統一モデルを構築できた． 核スピン分極の三重安定性は理論的に予言されただけであったため，実験的な観測を目指して定常発光測定を行った．提案理論では電子－核スピン間の相関時間が非常に重要であるため，実験では試料温度の変化からこれの制御を試みた．実験結果は相関時間が制御されたことを示唆したが，三重安定性の発見には至らなかった．一方で，相関時間の変化に伴って核スピン分極の双安定曲線が一重から二重なる様子を初めて観測した．
    構築した新規モデルでは異常ハンル効果が起きるVoigt配置だけでなく，Faraday配置で観測される核スピン分極の双安定性，三重安定性も再現できることを確認した．これにより初期の目的が1年目で達成できたと言える．この成果は２つの論文として投稿予定で，現在準備中である．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2020/04 -2024/03 
    Author : 笹倉 弘理, 足立 智, 小田島 聡, 鍜治 怜奈, 熊野 英和
     
    本研究課題は量子ネットワークの形成に向けた基盤技術として, 現行の光通信網と整合性が良く, 統計的・エネルギー揺らぎを抑制した量子ドット内蔵型光ファイバーデバイスを開発し, 伝送路の不安定性に対する耐性に優れたエンタングルメン伝送路の揺らぎの影響を受ける光子一つと真空場で形成されるエンタングルメントを介した量子テレポーテーションの実験を通して, 伝送路の揺らぎに対する忠実度の影響を精査し, 現行の光通信網を介した量子ノード間制御への展開を図るものである. 初年度及び2年目の実施計画は, 1. クロスニコル型量子ドット結合型光ファイバーデバイス(QDinF)の開発, 2. ナノピラー形状の最適化による単一偏波ファイバーへの光学結合効率の向上と境界面での偏光乱れの抑制, 3. 共鳴励起によるエネルギー揺らぎを抑制した単一光子生成手法の確立である. 初年度に引き続き, 偏光選択が可能な半導体量子ドット光ファイバーデバイスの開発を実施した. 偏波面を直交させた単一モード偏波ファイバー対に半導体量子ドットを装着した際に生じる消光比の低下を抑制するため, 半導体量子ドット成長膜表面へのワイヤーグリッド偏光子の形成を行った. 消光比の向上には, 偏光子の多層化が有効であることが予想されることから, 本年度は2層構造のワイヤーグリッドを作製し, 消光比を実測した. 典型的なインジウムヒ素/ガリウムヒ素量子ドットの発光波長である1マイクロメートルを対象として, ワイヤーグリッドを構成する金属の厚さ・幅, 周期, ワイヤーグリッド層間の厚さなどの構造を厳密結合波解析法による数値シミュレーションと実測結果を踏まえ検討した. ガリウムヒ素表面に2層構造のワイヤーグリッドを形成した結果, 500:1の消光比を実測した.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
    Date (from‐to) : 2021/07 -2023/03 
    Author : 足立 智
     
    2021年度7月の採択決定後，以下の研究を実施した． １．AlGaAsバルクの2次元TRKRマッピング：スピンノイズ分光の標準サンプルとして，研究例の少ないnドープAlGaAsバルク(Al=0.15)を選択した．まず，時間分解カー回転(TRKR)と全光核磁気共鳴(AONMR)分光を行い，電子・核スピン結合系ダイナミクスの基礎データを取得した．GaAsと比較して，電子ｇ因子，核スピン形成時間，核スピン緩和時間などの大きな違いを検出した．電子ｇ因子は+0.173とGaAsとは符号が異なり，絶対値も半分以下(GaAsの電子ｇ因子は-0.44)であるが，観測される核スピン分極は核磁場として1.4 Tに達する（GaAsでは～0.1 T）．nドープGaAsバルクでのスピン結合系ダイナミクスのパラメータは大きく異なるが，同じ形成モデル（基盤研究Bで開発した統一的な電子・核スピン結合系ダイナミクスモデル）で説明できることが分かった．これらの基礎データはスピンノイズ分光データと比較して，そのデータ検証に用いることができる．これらの結果は学会発表したが，Al密度依存性を加えて論文として準備中である． ２．スピンノイズ分光光学系の構築：基礎データの取得がほぼ終了したので，スピンノイズ分光系を既存のTRKR分光系に組み込んだ．長時間測定が必要なので，冷凍機型のクライオスタットを使用し，スピンノイズ測定を行った．磁場印加の有無での差を取ることで，スピンノイズの検出に成功したが，S/N比向上のための電気ノイズの低減，リアルタイムスペアナでの同時観測帯域シフトなどが必要で，その計測プログラムの作成を急いでいる．更に，もう１つの試料として選択したErドープYSO結晶について，フォトンエコーなどの時間域分光，ホールバーニングなどの周波数領域分光を行い，基礎データを取得すると同時に学会発表可能な多くの成果を得た．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2020/04 -2023/03 
    Author : 鍜治 怜奈, 足立 智
     
    スピンノイズ・核磁気共鳴法（SNS-NMR）法の開発と核四極子相互作用（NQI）チューニングの実証に向けて，令和3年度は以下の成果を得た： 1）令和2年度はn-GaAsバルクで実験を進めたが，試料選択の幅を広げるためにn-AlGaAsバルク（Al濃度：15%）に注目した．まずは時間分解カー回転分光法（TRKR）を用いて，電子g因子とスピン緩和時間を評価した．次に斜め磁場配置のTRKR測定で光誘起核スピン分極（NSP）の有無を確認したところ，外部磁場を大きく上回る核磁場が形成されていることが分かった．また，TRKRパルスシーケンスの一部を変更して核磁場の形成・緩和時間を評価したところ，これら時定数がn-GaAsに比べて長いことが分かった（学会発表済み）． 2)令和2年度に引き続き，歪みデバイスの作製を進めた．圧電素子で発生した歪みをナノピラー化した半導体試料に伝播させるために，ガラス成型機による熱圧着を試したが，発光効率の低下が問題となったため熱圧着条件の絞り込みは中断，透明レジスト材料（今回はHSQを使用）のスピンコートで固定する方法に切り替えた．その後，圧電素子の場所依存性やHSQのコート条件を調べることで，熱圧着過程を含まなくても量子ドット（QD）に外部歪みを伝播させることに成功した（学会発表済み）． 3）NQIが光誘起NSPに与える影響を調べるため，単一QDの時間分解ハンル測定を実施した．これまでQDにおけるNQIの主軸は結晶成長軸と同軸と考えられてきたが，今回の実験結果から，NQIが面内成分を持つことが示唆された．これは自己集合QDで観測される巨大面内NSPの形成メカニズム解明につながる重要な発見であり，学術誌への投稿準備を進めている． 上記3点に加えて測定系の改良・整備にも着手したが，SNS信号取得には至らず，最終年度の課題として持ち越すことになった．
  • Japan Society for the Promotion of Science：Scientific Research B
    Date (from‐to) : 2019/04 -2022/03 
    Author : TAWARA Takehiko
  • 半導体ナノ構造での自発分極を利用した核スピン完全偏極
    日本学術振興会：挑戦的研究（萌芽）
    Date (from‐to) : 2017/04 -2019/03 
    Author : 足立 智
  • 光学的核スピンエンジニアリングと局在スピン操作
    Japan Society for the Promotion of Science：Scientific Research A
    Date (from‐to) : 2013/04 -2017/03 
    Author : Adachi Satoru
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2015/03 
    Author : TODA YASUNORI, ADACHI Satoru, NAKAYAMA Masaaki
     
    Spatiotemporal four-wave mixing (FWM) spectroscopy of semiconductor excitons was developed by using (A) variably controlled Laguerre-Gaussian (LG) pulses, (B) orbital angular momentum (OAM) resolved spectroscopy with high precision. The observed exciton OAM dynamics indicates that (1) near perfect OAM transfer to the exciton center-of-mass motion is achieved using the LG pulses with nonzero OAM, (2) imperfect conversion becomes significant when the excitation pulses include an OAM-free component (3) an extremely long OAM decay was observed in the bulk sample, which implies a small spatial variation of the exciton dephasing. Moreover, the topological charge dependence of the OAM dynamics suggests a robustness of the exciton OAM. For the application of the topological transformation, a novel spatially modulated optical feedback in a vertical-cavity surface-emitting laser was demonstrated for the first time, where the results show high selectivity of the OAM in the transverse mode.
  • 酸化エルビウム結晶におけるポピュレーション操作と量子メモリへの応用
    Japan Society for the Promotion of Science：Scientific Research B
    Date (from‐to) : 2012/04 -2015/03 
    Author : Tawara Takehiko
  • スピンコヒーレンスの新規検出法の実証と電子スピン高速制御への展開
    Japan Society for the Promotion of Science：Challenging Exploratory Research
    Date (from‐to) : 2012/04 -2014/03 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Scientific Research B
    Date (from‐to) : 2010/04 -2013/03 
    Author : ADACHI Satoru
     
    This study aims the manipulation of nuclear spins via hyperfine interaction by all-optical methods based on our previous studies, which is essential for the realization of the applications such as quantum gate operation, quantum memory, and quantum media conversion. For this purpose, in this year, we developed the following two techniques. This technique allowed us to measure the nuclear field fluctuations of ~40 mT and to clarify their influences to electron and hole spin relaxations experimentally and theoretically.
  • 量子ドットにおける核スピンの双安定性を利用した量子ビット変換
    財団法人テレコム先端技術研究支援センター：ＳＣＡＴ研究費助成
    Date (from‐to) : 2008/04 -2011/03 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2005 -2008/03 
    Author : ADACHI Satoru, TODA Yasunori, MUTO Shunichi
     
    In this project, we aimed the development of the technique to transfer the spin between the Zeeman-split electron states in a single quantum dot (QD). Then, we tried the following two methods; use of teraheltz wave and two-photon process via half-localized state in a QD. As a consequence, by the latter method, we succeeded the control of the exciton spin state and the details were published in the academic journals. In the experiments, depending on the light polarizations of the co-linearly propagating delay-controlled double pulses, we observed the in-phase and out-of-phase oscillations of photoluminescence (PL) from the Zeeman-split two exciton states. In the case of the out-of-phase oscillations, the oscillation of the Zeeman splitting energy as well as the magnitude of the PLs was observed. This is because the nuclear spin polarization in a QD was formed and followed the modulation of the electron spin polarization. This result indicates that the half-localized state of QDs is available as the intermediate state in the Lambda-type transition in order to control of the electron and nuclear spins. In addition, we investigated the hyperfine interaction between electron and nuclear spins in a single QD, and the bistability and hysteretic response of the nuclear spin polarization were observed in the dependence on excitation power, polarization, and external magnetic field. By using this nuclear spin switching, we proved that the effective g factor of the QD electron could be tuned widely from negative to positive and be set to zero.
  • 日本学術振興会：科学研究費補助金 萌芽研究
    Date (from‐to) : 2006/04 -2007/03 
    Author : 足立 智
     
    本研究では,可視〜紫外域発光素子,高パワー高周波デバイスなど次世代の高性能光・電子エレクトロニクス分野への多大な貢献が期待されている結晶材料であるGaNとZnOについて,基板材料との格子不整合に由来する歪のみならず,結晶のマクロ欠陥が引き起こす歪の空間分布を主に励起子の偏極度を通じて高感度2次元マッピングする計測手法を確立することを目的とした.具体的には,よく用いられる基板であるA面サファイア上に成長したGaN薄膜を試料として,スペクトル分解四光波混合法(FWM)による回折信号を,100ミクロン程度の空間分解能で取得した.FWMを用いる理由は,信号が励起子遷移の双極子モーメントの8乗に比例するため,微小な歪による励起子の偏極度変化が増幅されて検出できるためである.また種々の基板上に成長したGaN薄膜とバルク結晶について測定を行い、分裂エネルギーと強度比の相関から、検出された一軸歪の最小値として6H-SiC試料の結果を採用すると、10^<-5>のオーダーに達している。この値は一般的なX線回折装置で検出可能な最小歪量と同等であり、当初設定した目標値を達成した。対応する励起子の分裂エネルギーは100μeV、線形分光における強度比は1.1以下(FWM分光では強度比(1.1)^4〜1.5に増幅)に相当しており、通常の光学測定では有無を議論することの難しい歪検出を実現したことになる。また同一試料内での測定では、空間的に異なる歪の存在を明らかにすることができた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2007 
    Author : MUTO Shunichi, ADACHI Satoru, TSUCHIYA Takuma, SHIRAMINE Kenichi
     
    In this project, we did a feasibility study of memory applications of quantum mechanically superposed states of an ensemble of nuclear spins. In other words, we tried to clarify the possibility of quantum information storage using quantum bit (qubit) conversion of a photon to an ensemble of nuclear spins mediated by a single electron spin through hyperfine interaction. For this purpose, we had to realize the situation where energy at the flip-flop of electron and nuclear spins is conserved, that is, the cancellation of external magnetic field and the effective nuclear field. In 2006, we studied the formation of nuclear field as functions of intensity and degree of circular polarization of excitation light on a single InAlAs/GaAs quantum dot (QD). As a result, we observed hysteresis in the nuclear magnetic field as a function of intensity of the excitation light which is circularly polarized. We can interpret this phenomenon as a nuclear spin switching and we concluded that the cancellation of external magnetic field and the effective nuclear field was realized. This is a condition necessary for the electron nuclear spin qubit conversion. In 2007, we advanced our study to include the magnetic field dependence. Upon increasing field the nuclear field increased to a certain threshold value above which the nuclear field discontinuously decreased. Comparison with theoretical calculations tells us that the nuclear field completely cancelled the external magnetic field. Unfortunately, however, this nuclear field is determined by the balance of the formation and destruction of nuclear spin polarization, and is not indicating the perfect polarization or the nuclear dark state both of which can be used for the electron nuclear spin qubit conversion. This shows that the current status of InAlAs QD is not suitable for the qubit conversion and either enhancement of nuclear spin formation or reduction of spin deformation is needed.
  • 日本学術振興会：科学研究費補助金 萌芽研究
    Date (from‐to) : 2005/04 -2006/03 
    Author : 足立 智
     
    電子スピンと核スピン集団との相互作用(超微細相互作用)は半導体を使った量子演算で注目されている。超微細相互作用は、量子ドットの長い電子スピン緩和時間を最終的に制限するスピン緩和メカニズムと考えられ、またこの相互作用を通して、注入された電子スピンが引き起こす動的核分極により発生した核磁場は、電子エネルギー準位のシフト(オーバーハウザーシフト)を誘起する。特に量子ドットでは、電子の波動関数が局在するのでこの相互作用が桁違いに強い。 本研究では、これまで観測されていなかった自己集合量子ドットで光ポンピングによる核スピン偏極を初めて観測した。積層して量子ドットが成長可能な自己集合量子ドットで、核スピンの光ポンピングに成功した意義は大きい。励起強度に依存するが、単一InAlAs量子ドットからの発光が最大105マイクロ電子ボルトのオーバーハウザーシフトを示した。Voigt配置における励起子発光線の分裂を観測し、電子と正孔のg因子を評価したところ、核スピン偏極によって電子が感じる実効磁場は4.2テスラに及ぶことが分かった。これらにより、量子ドットがナノメートルサイズで強磁場を発生するナノマグネットとみなせることを実証した。同時に励起偏光に核スピン偏極率が制御可能であること、核スピン形成時間が最大10秒以内であることを実験的に見出した。すなわちナノマグネットのオン・オフが比較的短時間で光により行えることを意味しており、当初の研究目的を達成したと同時に、実用的にも意義深い結果を得た。 また量子演算における核磁場の新しい利用法として、従来g因子工学という手法で、材料と構造の組み合わせにより実現可能とされていた光スピン-電子スピン間のキュービット変換が、核スピン偏極による実効磁場でより柔軟性をもって実現できることを提案し、理論的に示すことにも成功した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2004 -2006 
    Author : TODA Yasunori, ADACHI Satoru, ARAKAWA Yasuhiko
     
    Since strain and defects in semiconductors directly connect with the device performance, the influence has been studied extensively so far. Generally, there are various types of defects ranging from an atomic to a microscopic scale depending on the substrate, structure and growth conditions. In addition, the local strain fields due to mismatches in the lattice constants and the defects/impurities are also important for the thin films grown on foreign substrates. Therefore, three-dimensional (3D) analysis with a high spatial resolution is necessary for the precise characterization. One approach to the optical characterization in 3D is the use of nonlinear processes, in which excitation well below the band-gap allows for cross-sectional analysis at any depth. Furthermore, the use of nonlinear spectroscopy often provides significant enhancement of the signal sensitivity. In this work, we demonstrated i) multiphoton induced absorption imaging and ii) four-wave mixing (FWM) spectroscopy for the precise characterization of Gallium Nitride (GaN) in terms of strain and defects. Both techniques developed here allow for nondestructive and noninvasive optical characterization not only for GaN but also for other semiconductor materials including nanostructures, which would be useful for diagnosing complex device structures. In the two-photon absorption (TPA) imaging, we successfully mapped out the 3D distribution of defects with high spatial resolution. Moreover, using transient TPA measurements, we were able to obtain precise TPA coefficient that is one of the useful parameters for evaluating the optical damage threshold. In the GaN films, we showed that localized regions exist with significantly higher TPA coefficients, possibly due to the concentrations of defect states on a microscopic scale. In another nonlinear spectroscopy based on degenerate FWM technique, we successfully mapped out the local strain-field very precisely. Since the diffraction signal in FWM increases as the fourth power of the exciton oscillator strength, the exciton spectra show strong polarizations resulting from the uniaxial strain in the sample. The highly polarized spectra allow us to determine the precise splitting energy imposed by the local strain and defects. We measured various samples including GaN films on isotropic substrates, and examined the lower limit of detectable uniaxial strain, which is comparable with the resolution of conventional X-ray diffraction analysis. Since the diffraction signal in FWM increases as the fourth power of the exciton oscillator strength, the exciton spectra show strong polarizations resulting from the uniaxial strain in the sample. The highly polarized spectra allow us to determine the precise splitting energy imposed by the local strain and defects. We measured various samples including GaN films on isotropic substrates, and examined the lower limit of detectable uniaxial strain, which is comparable with the resolution of conventional X-ray diffraction analysis.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2002 -2005 
    Author : MUTO Shunichi, ADACHI Satoru, TODA Yasunori, SHIRAMINE Kenichi, YOH Kanji
     
    An electron spin in a quantum dot is one of important candidates to be used for future large scale quantum computing. We have already proposed a set of universal quantum gates using photon-assisted tunneling and its coulomb blockade. In this project, we have done various experimental studies on the feasibility of this proposal. Also, the quantum computing is required to be connected to the photonic quantum infromation processing. Therefore we proposed a scheme to cunvert a photon qubit and an electron spin qubit and experimentally evaluated this proposal. Before experiments, we did computer simulation of our universal gates and found that the experimental demonstration of the CNOT gateis possible ifthe coheraice of an electron spin is largo-than 100 ps. Then, we developed a measurem ent technology based on the four-wave-mixing FWM to detarmine the electron spin coherence. We applied this to the spin relaxation measurements of electrons in a quantum well for which the pump -probe technique is established. The result of the new method, i.e. spin-diffracted FWM gave the same result as the pump -probe, indicating the validity of the method. We then, applied this to the ensemble of InAlAs/AlGaAs quantum dots and found that the longest coherence of these dots is as long as 7 ns. This value is much longer than those in the conventional method using streak-camera and indicates that the measurements of resonant excitation and dedection such as ours are necessary for precise determination of spin coherence instead of the non-resonant measurements such as those using streak-camers. We also proposed a new qubit conversion scheme using the nuclear field to realize the degenerate electron levels and energy-split hole levels in a quantum dot. By exerimentally realizing the nuclear field by optically orienting the electron spins in an InAlAs/AlGaAs quantum dot, we found that we can realize the band structure for a qubit conversion between a photon and an dectron spin.
  • 半導体量子ドットの電子スピンコヒーレンス制御と量子コンピューティングへの応用
    東電記念科学研究所：研究助成
    Date (from‐to) : 2001/04 -2004/03 
    Author : 足立 智
  • Hyperfine interaction in semiconductor quantum dots
    Date (from‐to) : 2004
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2001/04 -2003/03 
    Author : ADACHI Satoru, TANAKA Katsuhiko, TODA Yasunori
     
    Im present work, we aimed the estimation of the crystal quality via the detection of the phonon scattering by the defect and so on by using our developed phonon-polariton imaging technique. We have performed the imaging experiment for the LiTaO_3. The phonon generation and monitoring of the propagating polariton wavepackets have been imaged. Illuminating the delayed pulse into the crystal in order to probe the generated phonon-polariton wavepackets, we could construct the image of the wavepackets at the real time within the temporal resolution of the used pulse. The phonon polariotn is really the modulation of the refractive indices and therefore the phase object. Although it is impossible usually to detect the phase of the scattered light since our detection ability is sensitive only to the intensity of the light, the conversion from the phase information to the intensity information can be achieved by using Talbot effect. We have succeeded to capture the interference of the phonon polariotn wavepackets at the real time via the special arrangement. Also we could control the amplitude of the propagating phonon polariton wavepacket within some extent. The obtained results can contribute greatly to the phonon spectroscopy and indicated the new direction of the research. By using the similar four-wave mixing technique, we could estimate the sample quality of the bulk GaN, which is the promising material for the laser diode and so on, via the phonon scattering and exciton-exciton interaction, and found the heterobiexciton. The hetero biexciton consists of the heavy-hole and light-hole excitons and we found the heterobiexciton in GaN for the first time.
  • 量子構造半導体でのスピン拡散のイメージングと拡散機構の解明
    財団法人テレコム先端技術研究支援センター：ＳＣＡＴ研究費助成
    Date (from‐to) : 2001/04 -2003/03 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2002 -2003 
    Author : MUTO Shunichi, SHIRAMINE Kenichi, TODA Yasunori, ADACHI Satoru, TAKEUCHI Atsushi
     
    Self-assembled InAlAs/AlGaAs quantum dots are grown by the Stranski-Krastanow mode of Molecular Beam Epitaxy (MBE). We measured the spin relaxation time of the structure under the non-resonant optical excitation by using 80 fs pulses by the titanium sapphire laser at wavelength of 780 nm. We used the right circular polarized light for the excitation of carrires to obtain fixed electron spins. The luminescence from the quantum dots at 10 K was divided into the right circular and the left circular components and was temporary resolved by the streak-scope. While the lifetime of the exciton was about 1 18 ns, the spin relaxation time determined by the decay of the polarization of luminescence was 1.31 us, which is comparable to the lifetime. The result indicates that the major relaxation mechanisms in the quantum well are not effective in the quantum dots and that the quantum dot is a good material for the coherent control of electron spins. As the spin-electronisc material for the future generations, wide-gap semiconductors and a polymer was studied with emphasis on the magnetic or spintronic properties.
  • Control of spin coherence in nanostructures
    JST Basic Research Programs (Core Research for Evolutional Science and Technology :CREST)
    Date (from‐to) : 2003
  • フォノンイメージングによる誘電体結晶評価システムの構築
    日本板硝子材料工学助成会：研究助成
    Date (from‐to) : 2001/04 -2002/03 
    Author : 足立 智
  • 整形パルスによる誘電体結晶中での伝播波束の制御とイメージング
    カシオ科学振興財団：研究助成
    Date (from‐to) : 2000/04 -2002/03 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2000/04 -2002/03 
    Author : ADACHI Satoru
     
    In recent years, people have much interest on "spin electronics" such as spin transistors, where electronic spin plays more important role than its charge in semiconductors. Then knowledge of the spin relaxation and spin diffusion is one of keys for success. Nevertheless those physical mechanisms in quantum structures are not well known. Under this background, We studied the diffusion and relaxation of exciton spin in quantum well structures. For this purpose, we utilized the four-wave-mixing spectroscopy with spin grating. Two pump pulses generated the exciton density grating near the sample surface in the co-linear polarizations. For the cross-linear polarizations, the pump pulses cannot interfere and therefore uniform exciton density is created. But the mixture of up-spin and down-spin of exciton changes according to the spatial position and thus the spin grating can be created. The pitch of both density and spin gratings can adjust by the crossing angle between the pump pulses. The time-delayed probe pulse diffracted from those gratings gives the decay rate of the gratings that includes the information about the relaxation and diffusion of the spin and density according to the character of the created grating. So, we could measure the spin relaxation ; spin diffusion constant, recombination and density diffusion constant in the same system. In the result, we obtained that spin diffusion rate is 3.5-times larger than density diffusion. This result is for the first time under my knowledge.
  • 高時間分解反射型空間イメージング法の開発と量子構造半導体における励起子スピン拡散への応用
    村田学術振興財団：研究助成
    Date (from‐to) : 2000/04 -2001/03 
    Author : 足立 智
  • 高強度レーザーのパルス整形技術の開発と応用
    大阪大学レーザー核融合研究センター：共同研究
    Date (from‐to) : 2000/04 -2001/03 
    Author : 足立 智
  • 熱非平衡状態下でのレーザー誘起格子振動を利用した不純物ドーピングに関する研究
    生産技術研究奨励会：旅費支援
    Date (from‐to) : 1999/04 -2000/03 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2000 
    Author : TAKEYAMA Shojiro, ADACHI Satoru, MINO Hirofumi, NAKAYAMA Takashi
     
    1.Biexciton states realized in diluted magnetic semiconductor quantum structures have been investigated under high magnetic field. The destabilization of a singlet biexciton has been observed for the first time under extremely high magnetic field effectively induced by the exchange interaction through the diluted magnetic barrier, whereas a spin triplet biexciton increases its stability. A diffusion Monte-Carlo simulation taking monolayer fluctuation at the interface into account has been performed to evaluate the binding energies of the biexciton, which agreed well with the observation. 2.The exciton localization mechanisms in the dilute magnetic semiconductor quantum structure have been studied both magneto-photoluminescence measurements and theoretical magnetic polaron model. It has been clarified that an exciton bifurcation takes place caused by the polaron effect. 3.Enormous Zeeman shifts in diluted magnetic quantum wells have been observed by the magneto-luminescence study under high pressure and extremely high magnetic field. The results have been well accounted for by the interface δ-potential model. We have henceforth proposed the method of extracting monolayer magnetism at the hetero-interface in the dilute magnetic semiconductor hetero structures. 4.We could observe spin polarized charged excitons in high density two-dimensional electron gas system realized in the diluted magnetic quantum wells. Our analysis of the magneto-absorption and photo-luminescence measurements has led our comprehension of the creation and recombination mechanisms of the spin polarized charged excitons at such high electron density regime.
  • 固体中を伝播するフォノンポラリトンの2次元イメージングに関する研究
    実吉奨学会：研究助成
    Date (from‐to) : 1998/09 -1999/09 
    Author : 足立 智
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1998 -1999 
    Author : TAKAGI Yoshihiro, ADACHI Satoru
     
    We have developed a subpicosecond non-degenerate pump-probe spectrometer based on the optical sampling technique using a combination of asynchronous tunable femtosecond lasers. Owing to its simple instrumentation time evolution of subpicosecond to nanosecond excited molecular processes in solution and of exciton relaxation processes in semiconductor multiple quantum wells has been detected on an oscilloscope by an effective time base magnification of 760,000 times. Fast acquisition of the temporal profiles and ease of wavelength scanning allowed compilation of time-resolved absorption and excitation spectra. A possible extention of the spectrometer with one of the light sources being a synchrotron radiation instead of the femtosecond laser is discussed.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1997 -1998 
    Author : 高木 芳弘, 足立 智
     
    超短パルス光照射による磁性体中のコヒーレントマグノン生成のための観測手法を確立した。 研究結果の1:マグノン発生の起源であるコヒーレントフォノン(誘導ブリュアン散乱)の観測装置の製作と基本性能の評価。観測したいマグノンは磁気弾性効果や磁歪などを通して音響フォノンモードの一部として現れ、その振動数帯域は1MHz〜10GHzである。一方、発生するコヒーレントフォノンの強度は2本の励起光の入射角をほぼ平行にすることで高められる。このとき振動数はMHz帯域に下がるため、時間分解測定は必然的に計測器の応答範囲内で満足できる(第1法)。この場合、観測システムは光学遅延装置を要する高振動数帯域の場合(第2法)と異なる。第1法の観測システムを組み、種々の液体試料でコヒーレンド音響フォノンを検出した。実験結果から、励起光で発生する音響フォノンによる検出光の回折効率には、光吸収により形成される静的な熱回折格子が一種のヘテロダイン検波の役割を果たす寄与が大きいことを見出した。本装置の検出感度(最小回折効率)は10^<-4>で、マグノンの検出には更に3桁の改善を要する。一方、第2法は光路長の長い光学遅延装置を要するが、これを作成し、高繰返しパルスレーザーを用いることで感度が2桁改善された。 研究結果の2:マグノンをはじめ光パルス照射による磁化応答の磁気的検出法に関連した測定。 磁気検出法の試みでは、磁性半導体CdCr_2S4、CdCr_2S_4、HgCr_2SeSe_4の3種の試料で光パルス照射による高速応答する誘起磁化を検出した。特にキュリー点直上での常磁性〜強磁性の光誘起転移効果を後者の2つの物質で初めて見出した。用いた検出コイルの時間応答は高々1ナノ秒であり、マグノンの検出にはギガヘルツ帯以下で適用可能である。本研究期間中主に観測装置の感度向上に専念した結果、コヒーレントフォノンを介した磁性の動的過程の観測法の有用性が確認されたので、マグノン信号の検出に向けて研究を継続する。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1995 -1995 
    Author : 足立 智
     
    まず本年度は昨年までに開発した光サンプリングポンプープローブ分光システムの性能向上を目指すとともに、チャープパルスサンプリング法の開発に取り組んだ。チャープパルスを生成する方法として1枚の回折格子を用いる方法と光ファイバー中で起こる自己位相変調効果を利用する方法とを実験的に比較した。その結果、双方で100ピコ秒程度のパルスが得られたが、システムをコンパクトにするため後者を選択した。高価なストリーク管の代用としてオシロスコープブラウン管の改造を考えていたが、ブラウン管だけを購入することが困難でありこれの使用を断念した。チャープパルスを使って周波数スペクトルを取得する代わる別の光サンプリング法の性能向上案として測定感度の向上を試みた。現状ではロックインアンプを使った通常のポンプープローブ法に比べて1桁以上感度が悪い。これを改善するため2台のフェムト秒レーザーをパルス幅程度のジッター内で同期させ他方に対しもう一方のレーザーの繰り返し周期に変調をかけ位相敏感検波を行う方法に切り替えた。現在2台のフェムト秒レーザーをパルス幅程度のジッター内で同期させる試験が終了したところである。その結果約2ピコ秒以内で同期が可能であることが分かった。その他現状の光サンプリング法を用いた溶媒和過程に関して裏面2の研究、量子井戸構造半導体のスピン緩和に関して裏面1の研究を、さらにその温度依存性を測定し緩和メカニズムを特定した研究成果をPhysical Review Lettersに投稿できた。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1994 -1994 
    Author : 足立 智
     
    本年度の研究計画として 1)ジッターフリーポンプープローブ光学系の構築 2)性能評価と物性測定への応用を挙げた。現時点で1)および2)の両方を完了している。従来のポンプープローブ法に比べて本分光法は厳密に2台のフェムト秒レーザーを同期させる必要がない、ポンプ光とプローブ光の波長の組合せを全く任意に選択できる、簡単な操作で瞬時に観測したい時間領域(13ナノ秒からサブピコ秒まで)を変更できる、モーター駆動の光遅延系を用いないので機械的ノイズの影響を受けない等の利点を持っている。 まずこの分光法を用い、有機色素(HDITCI)を試料としてダイナミックストークスシフトの測定等を行い、ナノ秒(レーザーの繰り返し周波数で制限、現在13ナノ秒)領域からサブピコ秒領域までの広い時間領域にわたって種々の励起およびプローブ波長の組合せで輻射緩和、回転緩和、溶媒の配向緩和、分子内再分配(IVR)に関する知見を得た(Dual wavelength optical sampling technique for ultrafast transient bleaching spectroscopy,to be published in Optics Communications)。 次にGaAs/AlGaAs多重量子井戸構造半導体を試料とし、そのスピン緩和を室温で測定することに成功した。重い正孔励起子を共鳴励起した場合の結果はロックインアンプを用いた従来の方法での結果と一致した。また軽い正孔励起子を共鳴励起し、重い正孔励起子のエネルギー位置でプローブした場合、スピンのメモリーが測定のS/Nの範囲では完全に消失していることが分かった。現在さらに検出感度を挙げる努力をするとともに、試料を低温に保ちスピン緩和のダイナミクスについてスピンメモリーの伝達に注目して研究を行っている。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1993 -1993 
    Author : 足立 智
     
    以下で述べる分光法の現地は申請時の研究計画で述べた原理とは多少異なるが、実際に種々の実験した結果以下の原理に基づいた方法の方がより優れていると判断し実行した。 2台のレーザーからのフェムト秒パルスは時間的に全く独立(非同期)であるため、これらを使ってポンプープローブ分光を行うには同期指せる必要は無いが2つのパルスの時間関係がはっきりしていなければならない。そこでポンプ光側レーザーのパルス幅を回析格子で130fsから60psまで伸延し、非線形結晶上でプローブ光と混合し和周波光を発生させた。伸延されたパルスは角度分散により時間によってそのkベクトルが異なるため和周波光はポンプ光とプローブ光とが時間的に結晶上一致したときのみ発生しそのkベクトルは一致したじかんにより異なる。すなわち時間を空間に変換できる。プローブ光には試料からの信号を含んでおり、従って和周波光にも信号成分が含まれる。和周波光のスポットの位置が時刻に、検出した強度が信号強度となる。実験では和周波光をCCD検出した。空間軸の直線性と空間分解能で時間軸の精度が決定され時間分解能が現状では2psであった。しかしこのままでは両方のパルスが全く同期していないので測定したい時間スケールに関係なくパルス周期を最大遅延時間とする測定となる。特に短時間領域の観測では測定能率が低下する。そこで広げたポンプ光パルス幅内に必ずプローブ光が到達する様、両レーザーに粗い同期えおかけた。この粗い同期は両パルスの折り返し周波数の差を検出して一方のょうのレーザーに取り付けたピエゾ素子を介して負帰還を加え共振器長を制御することにより達成した。今後の課題として時間分解能をパルス幅(130fs)程度まで向上させることが挙げられる。本方法では和周波光のスポットの大きさで時間分解能が制限されるため、プローブ光ビーム径を小さくする一方、回折格子ーレンズ間距離、およびレンズ焦点距離の最適化が必要である。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1992 -1993 
    Author : 高木 芳弘, 足立 智, 嶽山 正二郎, 高木 芳弘
     
    本研究では相関法による超短パルス光の測定を目的として、固体の光電効果における非線形応答を利用した新しい手法の実用化を試みた。初年度で指摘された問題点や明らかにされた点を挙げる。 1)実用上解決すべき点。市販の超短パルスレーザー装置では通常、数十メガヘルツのパルス繰返し率で出力が得られる場合が多い。平均パワー80mW、繰返し率76MHz、パルス幅100フェムト秒の出力はピーク強度は10kWで、ビーム断面積0.1cm^2を非集光で用いて100kW/cm^2である。この集光密度に対して非線形光電効果は単一パルスでも信号が得られるが、これが高い繰返し率で照射されると、光電変換後の電子の蓄積効果が現れ、応答出力は一次依存性が二次依存性を上回ってしまうことがセシウムアンチモンの光電陰極を用いて判明した。 光電効果は、入射光強度と用いる光電材料に依存して一次〜5次まで強度依存性が激しく変化することが判明した。これは使用する光強度領域を制限することになるので、分光感度特性と合わせてあらかじめ知っておく必要がある。 2)相関法における他の手法(2光子蛍光法や高調波発生法)では困難な条件下、すなわち波長400nm以下の紫外域では本手法が最も簡便かつ高感度であることがわかった。非線形光電効果はヨウ化セシウムの光電陰極を用いて、波長200nmの近傍では検出に要するパルス光の最小積分強度は10nJで、単一パルスで測定できた。また同材料で波長266nmのパルスと532nmのパルス、及び波長266nmのパルスと1064nmのパルスのそれぞれの組合せで交叉相関が得られた。このときの自己相関信号によるバックグラウンドとの強度比はほぼ100で、この結果、ある限られた波長範囲ではバックグラウンドフリーな相関測定が可能であることが明らかにされた。 3)本手法では自己相関や交叉相関の測定により光電陰極材料の評価を行ったが、調べられた時間応答特性は材料の光物性の研究試料にもなり得る。特にヨウ化銅やヨウ化タリウムにおいては伝導帯への光励起により伝導帯におけるエネルギー移動の動的挙動が顕著に現れた。 本研究は上記の解決すべき課題を依然残しており、研究期間終了後も平成6年9月30日までに完了させる予定である。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1992 -1992 
    Author : 高木 芳弘, 足立 智, 嶽山 正二郎, 高木 芳弘
     
    研究計画に沿い、磁性体の光キャリャー注入効果を調ベるたに先ず半導体GaAs/AlGaAsの量子井戸について光励起スピン配向の測定を行った。光源にパルス幅160fsのチタン・サファイアレーザーを用い、ハンド端の励起子共鳴吸収による吸収の過渡飽和を観測した。重い励起子の励起では従来の報告通り円偏光のセンスに対応した吸収飽和の減少及び増大が見出され、電子スピン±1/2の準位間のスピン緩和時間20psが得られた。一方、軽い励起子を励起した場合にも同様の吸収飽和における円偏光依存性が観測され、スピン緩和時間2ピコ秒が得られた。GaAs/AlGaAsについて軽い励起子のスピン緩和を直接観測したのは我々が最初である(発表予定)。また重い励起子ではスピン緩和時間の励起光強度依存性も新しく見出された。励起子の緩和については従来の報告により励起密度が高いと励起子の電子と正孔間のクーロン力が多数のキャリャーによってスクリーニングされることが指摘されているが、励起子スピンに関してもこれを反映しているかどうかはさらに詳しい実験を要する。 ポンプ・プローブ法による高速スピン緩和の測定法が確立できたので、本装置を用いて目的とする磁性半導体CdMnTeを低温で調ベた。励起子の共鳴エネルギーに同調させ、数ピコ秒の緩和波形が観測され、偏光依存性も見出された。本物質は透過で観測できないので反射による測定を行った。信号の偏光依存性はスピン選択性から期待されるものと一致しないので、現在、試料を薄膜にし透過で測定できるよう準備中である。 磁性絶縁体MrO単結晶についても光励起スピン配向を測定した。室温では常磁性で77Kでは反強磁性であるが、いずれの温度でもピックアップコイルによる磁化の検出方法では信号が得られなかった。室温ではナノ秒以下の速いスピン緩和により、また低温では強い交換力のため磁化の検出が困難になっていると思われるので時間分解能の改善が必要。

Educational Activities

Teaching Experience

  • Laser Spectroscopy
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 固体光物性, スピン，コヒーレンス，光との相互作用
  • Special Lecture in Applied Physics I
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 量子光学と量子力学，量子情報処理，単一光子，もつれ合い光子対，ベル測定
  • Laser Spectroscopy
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 固体光物性, スピン，コヒーレンス，光との相互作用
  • Electronics
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 線形回路，過渡応答，周波数解析，半導体，ダイオード，トランジスタ，サンプリング定理，離散時間フーリエ変換，量子化
  • Introduction to Applied Physics
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : ナノテク・ナノサイエンス、光科学、量子力学、複雑ネットワーク
  • Introduction to Applied Physics
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : ナノテクノロジー、光科学、複雑ネットワーク、電子顕微鏡、太陽系外惑星

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