MF研究者総覧

Researcher Database

Advance
Researchers' Page on researchmap
Last Updated :2024/09/13

Researcher Profile and Settings

Master

Affiliation (Master)

  • Faculty of Engineering　Applied Physics　Complex Material Physics

Affiliation (Master)

  • Faculty of Engineering　Applied Physics　Complex Material Physics

researchmap

Profile and Settings

Affiliation

  • Hokkaido University, Faculty of Engineering, Professor

Degree

  • Doctor of Science
  • Master of Science（Kyoto University）

Profile and Settings

  • Name (Japanese)

    Nomura

  • Name (Kana)

    Ryuji

  • Name

    200901011284712056

Affiliation

  • Hokkaido University, Faculty of Engineering, Professor

Achievement

Research Interests

  • superfluid   quantum solids   quantum liquids   Low-temperature physics   超流動   量子固体   量子液体   低温物理   

Research Areas

  • Natural sciences / Magnetism, superconductivity, and strongly correlated systems

Research Experience

  • 2021/06 - Today Hokkaido University Faculty of Engineering professor
  • 2024/09 - 2024/09 京都大学大学院理学研究科 物理学第一分野 非常勤講師
  • 2022/09 - 2022/09 Muroran Institute of Technology
  • 2021/08 - 2021/09 電気通信大学大学院情報理工学研究科 非常勤講師
  • 2016/04 - 2021/05 Tokyo Institute of Technology School of Science
  • 2020/04 - 2020/09 明治大学大学院理工学研究科 兼任講師
  • 2018/12 - 2018/12 日本女子大学大学院理学研究科 日本女子大学集中講義講師
  • 2007/04 - 2016/03 Tokyo Institute of Technology Graduate School of Science and Engineering, Department of Physics(Condensed Matter Physics)
  • 2000/04 - 2007/03 東京工業大学理工学研究科物性物理学専攻 助手
  • 1998/12 - 2000/03 Northwestern University research fellow
  • 1996 - 1997 :日本学術振興会 特別研究員（ＤＣ）

Education

  •        - 1998  Kyoto University  Graduate School, Division of Natural Science
  •        - 1998  Kyoto University
  •        - 1991  Kyoto University  Faculty of Science

Committee Memberships

  • 2024/07 -2024/07   The 2024 International Symposium on Quantum Fluids and Solids (QFS24)   International Advisory Committee
  • 2022/08 -2022/08   International Conference on Ultra Low Temperature Physics (ULT2022)   Organizing committee, conference vice chair
  • 2017/05 -2017/05   International Conference on Topological Material Science 2017   Local committee
  • 2014/12 -2014/12   International Conference on Topological Quantum Phenomena   Organizing committee
  • 2013/10 -2013/10   Second International Workshop for Young Researchers on Topological Quantum Phenomena in Condensed Matter with Broken Symmetries   Vice-chairperson
  • 2013/08 -2013/08   The International Conference on Quantum Fluids and Solids (QFS2013)   Organizing Committee
  • 2012/05 -2012/05   International Conference on Topological Quantum Phenomena   Organizing committee
  • 2011/11 -2011/11   International Workshop for Young Researchers on Topological Quantum Phenomena in Condensed Matter with Broken Symmetries   Chairperson

Awards

  • 2023/12 The Physical Society of Japan JPS Hot Topics
     Robust Quantization of Dripping Periods of Superfluid 4He, J. Phys. Soc. Jpn. 92, 124601-1-5 (2023) 
    受賞者: R. Nagatomo;K. Onodera;S. Kashimoto;Y. Aoki;R. NomuraSuperfluid 4He droplets exhibit robustly quantized dripping periods despite gradually varying input flow rates owing to their high amplitude and undamped oscillation.
  • 2022/08 International Conference on Ultra Low Temperature Physics (ULT2022) Best poster award
     Dripping character of superfluid 4He droplets 
    受賞者: Keita Onodera
  • 2017/06 The Physical Society of Japan JPSJ Editors’ Choice
     J. Phys. Soc. Jpn. 86, 074603-1-5 (2017)
  • 2014/12 Institute of Physics IOPselect
     New J. Phys. 16, 113022-1-9 (2014)
  • 2013/09 Low Temp. Phys. Editor's Picks in Low Temp. Phys.
     Low Temp. Phys. 39, 780-785 (2013)
  • 2013/05 The Physical Society of Japan J. Phys. Soc. Jpn., 2012 Highly Cited Article
     J. Phys. Soc. Jpn. 80, 013602 (2011)
  • 2013/03 The Physical Society of Japan “Surface Majorana Cone of the Superfluid 3He B Phase” J. Phys. Soc. Jpn. 80, 013602 (2011)
  • 2012/12 東京工業大学理学系 平成24年度東京工業大学理学系若手研究奨励賞
     トポロジカル超流動ヘリウム3の表面マヨラナコーンの発見
  • 2011/12 The Physical Society of Japan JPSJ Editors’ Choice
     J. Phys. Soc. Jpn. 80, 013602-1-4 (2011)
  • 2011/01 The Physical Society of Japan JPSJ Editors’ Choice
     J. Phys. Soc. Jpn. 80, 123601-1-4 (2011)
  • 2007/09 日本物理学会 第一回日本物理学会若手奨励賞
  • 2006/02 The Physical Society of Japan JPSJ Editors’ Choice
     J. Phys. Soc. Jpn. 75, 023601-1-4 (2006)

Published Papers

  • Ryuma Nagatomo, Keita Onodera, Shiro Kashimoto, Yuki Aoki, Ryuji Nomura
    Journal of the Physical Society of Japan 92 (12) 0031-9015 2023/12/15 [Refereed][Not invited]
  • Ryuma Nagatomo, Keita Onodera, Shiro Kashimoto, Yuki Aoki, Ryuji Nomura
    JPS Hot Topics 3 124601-1 - 124601-5 2023/12 [Refereed]
     
    Superfluid 4He droplets exhibit robustly quantized dripping periods despite gradually varying input flow rates owing to their high amplitude and undamped oscillation. Since “superfluid” is already placed at the beginning of the sentence, “as a result of superfluidity” may be removed here.
  • Keita Onodera, Ryuma Nagatomo, Shiro Kashimoto, Ryuji Nomura
    Journal of the Physical Society of Japan 91 (6) 065005-1 - 065005-2 0031-9015 2022/05/27 [Refereed][Not invited]
  • Mutsuki Saito, Ryunosuke Takagishi, Nobuyuki Kurita, Masari Watanabe, Hidekazu Tanaka, Ryuji Nomura, Yoshiyuki Fukumoto, Kazuhiko Ikeuchi, Ryoichi Kajimoto
    Physical Review B 105 (6) 064424-1 - 064424-15 2469-9950 2022/02/17 [Refereed]
  • R. Nomura, Y. Okuda
    Reviews of Modern Physics 92 (4) 0034-6861 2020/12/02 [Refereed][Invited]
  • Crystallization Onset of Liquid Pockets via Mass Flow through Solid 4He in Aerogel
    R. Nomura, H. Matsuda, Y. Okuda
    J. Phys. Soc. Jpn. 88 035003-1 - 035003-2 2019 [Refereed][Not invited]
  • Crystallization of 4He in Aerogel with Warming
    R. Nomura, H. Matsuda, Y. Okuda
    J. Phys. Soc. Jpn. 87 115001-1 - 115001-2 2018 [Refereed][Not invited]
  • Taichi Yoshida, Akira Tachiki, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 (7) 0031-9015 2017/07 [Refereed][Not invited]
     
    A He-4 quantum crystal can be grown from a superfluid liquid extremely quickly owing to the high crystallization rate at sufficiently low temperatures. Such crystals are readily deformed by an applied force as the result of the crystal superfluid phase transition but, to date, the remotely controlled movement of highly deformable He-4 crystals has yet to be demonstrated. The present work attempted to move He-4 crystals using inchworm driving, a technique that is employed to impart motion to classical solid objects based on the difference between static and dynamic friction forces. Using a plate oscillating with a sawtooth-like non-symmetric motion 100 times over the span of 1.0 s, it was found possible to move a He-4 crystal on the plate in a superfluid at 0.3 K. However, the observed behavior was quite different from the ordinary inchworm driving of a classical object. Initially, one side of the crystal was seen to stick on the plate, and the crystal did not move for 0.6 s but rather deformed appreciably. After this deformation, the entire body of the crystal began to move, but the distance traversed was one order of magnitude larger than expected from the oscillation amplitude. This peculiar behavior is specific to this quantum crystal. The initial lack of motion can possibly be explained by pinning and depinning of the contact line on the substrate plate, while the extent of motion is attributed to the crystal superfluid transition, namely crystallization on one side and melting on the other, assisted by superflow induced during the oscillation process.
  • Ryuji Nomura, Haruka Abe, Yuichi Okuda
    New Journal of Physics 19 (2) 1367-2630 2017/02/01 [Refereed][Not invited]
     
    The relaxation dynamics of the crystal-superfluid interface of 4He after deformation induced by acoustic radiation pressure was investigated for various crystal orientations. The melting relaxation after growth was approximately 10 times slower than the growth relaxation after melting for vicinal surfaces and facets, while both relaxation times were consistent with each other for rough surfaces. The asymmetry in the time constant between the melting and growth of vicinal surfaces and facets can be qualitatively explained as the effect of superflow induced by local rapid interface motion, such as a quick rounding of facet edges of the 4He crystal. Rough surfaces move more isotropically and no significant local rapid interface motion is induced therefore, their relaxation is likely to be symmetric with a minimal effect of superflow. While the growth relaxation was simply back to the initial shape in a single stage, the melting relaxation was much more complex with multiple stages and the exhibition of various anomalous shapes depending on temperature. Anomalous shapes such as needle-like shapes during melting have a larger curvature and higher energy and thus should have disappeared more quickly than the growth shape with a smaller curvature, but they were considerably stable and disappeared slowly. This counter-intuitive asymmetry suggests the significant role of superflow in the relaxation process.
  • Takuya Takahashi, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 185 (3-4) 295 - 304 0022-2291 2016/11 [Refereed][Not invited]
     
    He crystals usually sink to the bottom of the container in a superfluid and are deformed into a flat shape by gravity when their size is much larger than the capillary length of 1 mm. When gravity is reduced to zero, the capillary length diverges and the gravity-flattened crystals are expected to relax into an equilibrium crystal shape determined by the interfacial free energy at low enough temperatures where the relaxation time is very short. We performed a reduced gravity experiment on He crystals at ultralow temperatures by developing a specially designed He-He dilution refrigerator compatible with the experimental restrictions in a small jet plane. He crystals relaxed to the equilibrium crystal shape below 600 mK during a reduced gravity period of 20 s produced by a parabolic flight. The equilibrium crystal shape, however, was metastable in most cases, governed by the boundary conditions imposed by the wall. Utilizing acoustic radiation pressure, we deformed the crystal enough to allow it to escape from the metastable shape below 150 mK. After this large deformation, the crystal relaxed to a shape completely different from its initial shape, showing three types of facets, viz., c-, a-, and s-facets, which was concluded to be the lowest energy equilibrium shape.
  • H. Matsuda, A. Ochi, R. Isozaki, S. Minami, R. Nomura, J. Pollanen, W. P. Halperin, Y. Okuda
    PHYSICAL REVIEW B 94 (2) 2469-9950 2016/07 [Refereed][Not invited]
     
    The phase boundary between the quantum solid and the liquid phases of He-4 is strongly modified in a porous material. However the phase diagram at very low temperatures remains unexplored. We have used a variable-volume experimental cell with optical access to visualize the crystallization of He-4 in silica aerogels with independent control of the pressure and temperature. The onset of crystallization was investigated in two aerogel samples with differing porosity both by pressurization at constant temperature and by cooling at constant pressure. With isothermal pressurization we have established a low-temperature phase diagram for each aerogel, and we find that the equilibrium crystallization pressure is reduced with increasing aerogel porosity. Crystals also began to grow in the aerogel on cooling at fixed pressure below an onset temperature T-grow. We found that below this temperature the crystallization rate increased with decreasing temperature. The aerogel in our cell was surrounded by bulk crystals of He-4, and surprisingly Tgrow was found to be widely distributed when the surrounding bulk crystals were repressurized. In this experimental arrangement, crystallization within the aerogel on cooling requires mass flow from these exterior bulk crystals and is strongly influenced by the disordered structure at the interface between the bulk solid and the helium within the aerogel.
  • T. Takahashi, H. Minezaki, A. Suzuki, K. Obara, K. Itaka, R. Nomura, Y. Okuda
    PHYSICAL REVIEW E 93 (5) 2470-0045 2016/05 [Refereed][Not invited]
     
    To investigate whether it is possible to control the wetting of He-4 crystals on a wall in superfluid, the contact angles of He-4 crystals were measured on rough and smooth walls at very low temperatures. A rough wall was prepared in a simple manner in which a commercially available coating agent for car mirrors, which makes the glass surface superhydrophobic, was used to coat a glass plate. The contact angles of He-4 crystals were increased by approximately 10 degrees on the rough wall coated with the agent. Therefore, the increase in the repellency of He-4 crystals in superfluid was demonstrated to be possible on a very rough surface. The enhancement of the contact angles and a scanning electron microscopy image of the coated surface both suggest that a Cassie-Baxter state of He-4 crystals was realized on the surface; the crystals did not have full contact with the wall, but entrapped superfluid was present beneath the crystals in the hollow parts of the rough wall.
  • Takuya Takahashi, Haruka Ohuchi, Ryuji Nomura, Yuichi Okuda
    SCIENCE ADVANCES 1 (9) 2375-2548 2015/10 [Refereed][Not invited]
     
    Equilibrium crystal shape is the lowest energy crystal shape that is hardly realized in ordinary crystals because of their slow relaxation. He-4 quantum crystals in a superfluid have been expected as unique exceptions that grow extremely fast at very low temperatures. However, on the ground, gravity considerably deforms the crystals and conceals the equilibrium crystal shape, and thus, gravity-free environment is needed to observe the equilibrium shape of 4He. We report the relaxation processes of macroscopic 4He crystals in a superfluid below 200 mK under zero gravity using a parabolic flight of a jet plane. When gravity was removed from a gravity-flattened 4He crystal, the crystal rapidly transformed into a shape with flat surfaces. Although the relaxation processes were highly dependent on the initial condition, the crystals relaxed to a nearly homothetic shape in the end, indicating that they were truly in an equilibrium shape minimizing the interfacial free energy. Thanks to the equilibrium shape, we were able to determine the Wulff's originandthe sizeof thec-facet togetherwiththevicinal surfaceprofilenext tothe c-facet. Thec-facet sizewas extremely small in the quantum crystals, and the facet-like flat surfaces were found to be the vicinal surfaces. At the same time, the interfacial free energy of the a-facet and s-facet was also obtained.
  • Kouki Akiyama, Masahiro Wasai, Masataka Mashino, Takeru Nakao, Satoshi Murakawa, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 (6) 0031-9015 2015/06 [Refereed][Not invited]
     
    Transverse acoustic impedance was measured in the superfluid He-3 B phase in magnetic fields to investigate the magnetic response of the surface bound states on a diffusive wall. The peak structure of the impedance in the temperature dependence disappeared in 50mT and this disappearance is possibly a reflection of the gap distortion in the field.
  • S. Murakawa, A. Yamaguchi, M. Arai, M. Wasai, Y. Aoki, H. Ishimoto, R. Nomura, Y. Okuda, Y. Nagato, S. Higashitani, K. Nagai
    PHYSICAL REVIEW LETTERS 114 (10) 0031-9007 2015/03 [Refereed][Not invited]
     
    The transverse acoustic impedance of superfluid He-3 was measured in the A(1) and A(2) phases up to 13 T to investigate the surface states in nonunitary superfluids. The temperature dependence of the impedance was much larger in the A(1) phase than in the A(2) phase. This nonsymmetric behavior indicates that momentum exchange with walls for spin-down surface states is quite different from that for spin-up surface states. The spin-dependent response might be a reflection of an essential feature of the nonunitary states where gap amplitudes depend on spin states. Weak-coupling theories ignore any spin-dependent processes and do not account for the nonsymmetric behavior.
  • Ryuji Nomura, Taichi Yoshida, Akira Tachiki, Yuichi Okuda
    NEW JOURNAL OF PHYSICS 16 1367-2630 2014/11 [Refereed][Not invited]
     
    The crystal shapes of He-4 falling in superfluid were investigated using a high speed video camera. As they fell, the upper surface of the crystal became rough and the lower surface became faceted as a result of being subjected to an upward superflow which induced melting of the upper surface and crystallization of the lower surface. When it landed on the bottom, a pulse-like wave was observed to travel around the surface from the impact point before it transformed itself quickly to adjust to a new boundary condition. The behavior of a crystal when it passed by a small needle during its fall was also observed. The rim of the facet was pulled by the needle and protruded. The origin of this extended deformation is not understood at present, but the superflow around the crystal was possibly the origin of the interaction between the crystal and the needle.
  • T. Yoshida, A. Tachiki, N. Ishii, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 175 (1-2) 120 - 125 0022-2291 2014/04 [Refereed][Not invited]
     
    Shape and motion of He-4 crystals in superfluid placed on a transversely oscillating plate were investigated visually. The plate was glued onto a piezo post which was driven in a shear mode electrically. The purpose of the experiment was to drive a He-4 crystal by a piezoelectric device which can be used to drive ordinary solids by the inchworm method. Facets of a single He-4 crystal 3 mm in width were destroyed by a single sawtooth pulse of 1 ms duration at 0.4 K. In case of a larger crystal 7.5 mm in width and 0.8 mm in height, only one side of the crystal moved toward the center of the crystal, while the other side never moved despite application of 100 pulses at 10 ms intervals. Therefore, the crystal grew vertically and its height varied from 0.8 mm to about 1.4 mm during the pulses. This anisotropic behavior had nothing to do with the direction of the sawtooth driver. Many of the observed behaviors were puzzling, but it can be said that the crystals responded to the oscillation sensitively and the sawtooth pulse induced a very anisotropic motion of the crystal surface.
  • Aguri Ochi, Hirofumi Matsuda, Rei Isozaki, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 175 (1-2) 126 - 132 0022-2291 2014/04 [Refereed][Not invited]
     
    Crystal-superfluid interface of He-4 in aerogel was shown to advance smoothly in a high temperature creep growth region above 0.6 K. In this report, we focused on the shape of the growing interface in the region and attempted to analyze the roughness of interfaces. The growth of rough interfaces is very common in nature and is known to often follow a scaling law; roughness usually increases with time and saturates in the later stage. We measured the roughness w(t) defined as the standard deviation of the interface height as a function of time t. It was found that w(t) in 98 % porosity aerogel initially increased with t and decreased after a particular time in the later stage. The abrupt reduction of roughness in the end of crystallization is unusual if it is intrinsic in the crystallization in aerogel.
  • Ryuji Nomura, Satoshi Murakawa, Masahiro Wasai, Kouki Akiyama, Takeru Nakao, Yuichi Okuda
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 55 42 - 47 1386-9477 2014/01 [Refereed][Not invited]
     
    Topological superfluids and superconductors have been theoretically proposed, and it is now necessary to experimentally confirm their existence. Superfluid He-3 should be the ideal test subject for topological theories because its bulk state is established to be that of a spin-triplet p-wave superfluid. Surface Andreev bound states of superfluid He-3 were investigated by transverse acoustic impedance measurements and their linear dispersion was confirmed on a highly specular wall. The superfluid He-3 B phase was found to be a topological superfluid showing bulk-edge correspondence and a surface Majorana cone was confirmed on the surface. Possible manifestations of the Majorana nature of the surface states are discussed. (C) 2013 Elsevier B.V. All rights reserved.
  • H. Matsuda, A. Ochi, R. Isozaki, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS 39 (9) 780 - 785 1063-777X 2013/09 [Refereed][Not invited]
     
    Formation of superfluid liquid pockets of He-4 surrounded by He-4 crystals were observed in an aerogel of 96% porosity. The liquid pockets did not crystallize by application of pressure but crystallized via avalanche by cooling below a particular temperature. The crystallization by cooling was also observed when crystals occupied a smaller portion of the aerogel. Driving force for the crystallization by cooling and possible mass transport process are discussed. (C) 2013 AIP Publishing LLC.
  • Hirofumi Matsuda, Aguri Ochi, Rei Isozaki, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 171 (3-4) 295 - 301 0022-2291 2013/05 [Refereed][Not invited]
     
    Using a variable volume cell, we were able to crystallize He-4 in aerogels at a constant temperature. The entire crystallization process was monitored visually owing to the transparency of the aerogel. Two different crystallization processes of He-4 in aerogels were observed: creep at high temperatures and avalanche at low temperatures. In a 96 % porosity aerogel, we noticed that He-4 remained liquid in some parts of the cell even though other parts of the aerogel were completely crystallized. Once such a situation was formed, the application of additional pressure did not further crystallize the liquid. This is presumably because a supply path of He-4 atoms from the bulk crystal was blocked by the crystals in the aerogel. This leftover liquid, however, was found to begin to crystallize via avalanches when cooled below a particular temperature. If the crystallization pressure in aerogel is temperature independent at low temperatures as the bulk crystallization pressure, the crystallization by cooling is rather unusual. Possible explanations would be a decrease of the crystallization pressure in aerogel in the low temperature region, or the supersolidity of crystals in aerogel playing some role in mass transport.
  • H. Matsuda, A. Ochi, R. Isozaki, R. Masumoto, R. Nomura, Y. Okuda
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 87 (3) 1539-3755 2013/03/15 [Refereed][Not invited]
     
    Nucleation of 4He crystals from the metastable superfluid in high porosity silica aerogel was investigated by an optical measurement. Critical overpressures at which the first 4He crystal appeared during pressurization were measured 50 times at each temperature. Contrary to the intuitive pore-size-limited nucleation suggested in previous studies in small pores, the critical overpressure did show a characteristic temperature dependence, indicating that the critical size of nucleation is also temperature dependent. It is confirmed that quantum nucleation at low temperatures and thermal nucleation at high temperatures occur as in the case of bulk crystal. Nucleation in this high porosity material shows characters of nucleation in both bulk and pores. © 2013 American Physical Society.
  • Takuya Takahashi, Haruka Ohuchi, Ryuji Nomura, Yuichi Okuda
    NEW JOURNAL OF PHYSICS 14 1367-2630 2012/12 [Refereed][Not invited]
     
    By developing a refrigerator compatible with the parabolic flight of a small jet plane, He-4 crystals in a superfluid were obtained in zero-gravity conditions at 0.6 K. We report Ostwald ripening of these crystals in the superfluid after being splashed by acoustic waves. Ostwald ripening is a process in which smaller crystals melt and larger ones grow to minimize the overall surface energy. Under gravity on the ground, this ripening was not apparent because it stopped growing at a capillary length of about 1 mm; crystals at lower positions grew to minimize the gravitational energy. Without gravity, however, Ostwald ripening was observed up to the order of 10 mm, a much greater length than the 1 mm due to the infinitely long capillary length, exhibiting a novel evolution of the crystal shape driven solely by the surface energy. S Online supplementary data available from stacks.iop.org/NJP/14/123023/mmedia
  • Y. Okuda, R. Nomura
    JOURNAL OF PHYSICS-CONDENSED MATTER 24 (34) 0953-8984 2012/08 [Refereed][Not invited]
     
    Superfluid He-3 is an intensively investigated and well characterized p-wave superfluid. In the bulk Balian-Werthamer state, which is commonly called the He-3 B phase, the superfluid gap is opened isotropically but near a flat boundary such as a wall of a container it can harbor interesting quasi-particle states inside the gap. These states are called surface Andreev bound states, and have not been experimentally explored in detail. Transverse acoustic impedance measurement has revealed their existence and provided spectroscopic details of the dispersion of the bound states. Recent theoretical arguments claim that the surface Andreev bound states of the superfluid 3He B phase can be recognized as the edge states of the topological superfluid and be regarded as a Majorana fermion, a fancy particle which has not been confirmed in elementary particle physics. In this review, we present up-to-date knowledge on the surface Andreev bound states of the He-3 B phase revealed by acoustic spectroscopy and the possible realization of a Majorana fermion, along with related studies on this topic.
  • Takuya Takahashi, Ryuji Nomura, Yuichi Okuda
    PHYSICAL REVIEW E 85 (3) 1539-3755 2012/03 [Refereed][Not invited]
     
    The response of He-4 crystals to the rapid reduction of gravity down to practically zero in a superfluid was investigated visually, utilizing the parabolic flight of a jet plane. At a high temperature of 1.6 K, the shape of He-4 crystals in the bcc phase did not change with a reduction of gravity during a parabolic period of 20 s, due to the low crystallization rate. At lower temperatures, such as 0.63 K, where the crystallization rate is sufficiently high, the shape of He-4 crystals in the hcp phase changed significantly, relaxing to a quasiequilibrium shape under zero gravity, where the c facet became enlarged and the a facet emerged on the surface. The crystal did not detach from the sample cell wall at any time because the adhesive force manifested as partial wetting to the wall was sufficiently strong. Some crystals removed from the wall by an acoustic wave pulse were found to float and drift in the superfluid for approximately 4.2 s under zero gravity, although most of them were quickly reattached to the wall.
  • S. Murakawa, M. Wasai, K. Akiyama, Y. Wada, Y. Tamura, R. Nomura, Y. Okuda
    PHYSICAL REVIEW LETTERS 108 (2) 0031-9007 2012/01 [Refereed][Not invited]
     
    We have found that the surface specularity for He-3 quasiparticle scattering is closely related to the superfluidity and the Kosterlitz-Thouless (KT) transition of He-4 film adsorbed on the surface. The specularity is determined by measurements of the transverse acoustic impedance of bulk liquid He-3. The unique point of our system is that we can control the correlation among He-4 atoms in the film by changing the pressure of the bulk He-3. The observed KT transition temperature is significantly suppressed by increasing the pressure, which suggests a strong correlation effect on KT transition.
  • S. Higashitani, S. Matsuo, Y. Nagato, K. Nagai, S. Murakawa, R. Nomura, Y. Okuda
    PHYSICAL REVIEW B 85 (2) 1098-0121 2012/01 [Refereed][Not invited]
     
    We study the odd-frequency Cooper pairs formed near the surface of superfluid He-3. The odd-frequency pair amplitude is closely related to the local density of states in the low-energy limit. We derive a formula relating explicitly the two quantities. This formula holds for an arbitrary boundary condition at the surface. We also present some numerical results on the surface odd-frequency pair amplitude in superfluid He-3-B. Those analytical and numerical results allow one to interpret the midgap surface density of states, observed recently by transverse acoustic impedance measurements on superfluid He-3-B, as the manifestation of the surface odd-frequency state.
  • Hirofumi Matsuda, Ryota Masumoto, Aguri Ochi, Ryuji Nomura, Yuichi Okuda
    26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 1742-6588 2012 [Refereed][Not invited]
     
    In an aerogel contained in a flat glass tube, we measured critical overpressures at which the very first He-4 crystal appeared. Crystallization and melting were repeated 50 times at a constant temperature in a variable volume cell and the nucleation probability as a function of overpressure was obtained. An anisotropic S shape characteristic of the nucleation process was successfully observed.
  • T. Takahashi, R. Nomura, Y. Okuda
    26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 1742-6588 2012 [Refereed][Not invited]
     
    When a relatively large He-4 crystal sticking on a sample cell wall fell slowly along the wall with cooling, a number of small superfluid droplets or negative crystals spontaneously emerged in the host crystal. The negative crystals rose in the host crystal due to their buoyancy, and finally merged into bulk superfluid surrounding the host crystal. The rising velocity of the negative crystals was almost constant regardless of the host crystal's falling motion, even when the host stayed on the bottom of the cell.
  • Ryuji Nomura, Hirofumi Matsuda, Ryota Masumoto, Ken-ichi Ueno, Yuichi Okuda
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (12) 0031-9015 2011/12 [Refereed][Not invited]
     
    It is found from a crystallization rate measurement of He-4 in silica-aerogels that crystals grow via thermal activation in a high-temperature creep region and via macroscopic quantum tunneling in a low-temperature avalanche region. Avalanche size distribution follows a power law in a 98% porosity aerogel and indicates that the system is in a self-organized critical state (SOC) in the growth regime via quantum tunneling. Temperature dependence of the exponent of the power law and the large-scale cutoff are also obtained. This is the first observation of SOC in macroscopic quantum tunneling phenomena.
  • Takuya Takahashi, Motoya Suzuki, Ryuji Nomura, Yuichi Okuda, Koji Kamiya, Takenori Numazawa, Peter Shirron
    MICROGRAVITY SCIENCE AND TECHNOLOGY 23 (4) 365 - 372 0938-0108 2011/11 [Refereed][Not invited]
     
    Superfluid He-4 was produced on a small jet plane for the first time using a small GM-refrigerator to condense the liquid and a scroll pump to get the superfluid by evaporation. The surface wave on superfluid under 0.5g (E), 0.1g (E) and 0.05g (E), together with 2g (E) and 1g (E), was successfully examined by an optical method utilizing parabolic flight. Here, g (E) is the gravitational constant on the ground. Assuming that only the fundamental mode was excited as determined by the sample cell width, the resonance peak in the frequency domain was well reproduced by the gravity wave with corresponding gravity constant.
  • Ryota Masumoto, Ken-ichi Ueno, Hirofumi Matsuda, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 162 (5-6) 399 - 406 0022-2291 2011/03 [Refereed][Not invited]
     
    Crystallization of He-4 in aerogels of 90 and 96% porosities shows a dynamical phase transition at around 600 mK due to the competition between thermal fluctuation and disorder: crystals grow via creep at high temperatures and via avalanche at low temperatures. In a very high porosity 99.5% aerogel, however, the transition had not been observed in our previous publication (Nomura et al. in Phys. Rev. Lett. 101:175703, 2008). We improved the spatial resolution of the video image and found that the 99.5% aerogel did have the transition at around 200 mK, which is much lower than those of the lower porosities. The avalanche size is significantly smaller in the 99.5% aerogel. The reduction in the transition temperature and avalanche size may be the consequence of weaker disorder for the crystallization in the very high porosity aerogel.
  • T. Takahashi, M. Suzuki, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 162 (5-6) 733 - 739 0022-2291 2011/03 [Refereed][Not invited]
     
    The gravity on the Earth (g (E)) has not been taken seriously to mask the fundamental phenomena on quantum solids, though there are some important studies on the critical phenomena of superfluid He-4 under microgravity. We are planning to investigate the effect of gravity on the equilibrium shape of solid He-4. Since we had a chance to do such an experiment on a small jet plane through the ground based program by JAXA, we got started to construct a cryostat which could cool down as low as 500 mK and meet severe restrictions of experiments on a jet plane. The main part of the refrigerator was a usual He-3-evaporator pumped by a scroll pump. A small GM refrigerator was installed to provide 4 K stage. 1 K pot was also put in which was also pumped by another scroll pump to condense He-3 gas and sample He-4. The cryostat was designed to have two optical windows to be able to observe solid He-4 under microgravity. In the test flight for the refrigerator, the minimum temperature of 690 mK was kept during the entire flight of two hours in which 7 to 8 times parabolic flight was performed. Each parabolic flight includes about 20 seconds microgravity and 20 seconds 1.5 to 2.0 g (E) period before and after the microgravity. We did some preliminary experiments with bcc solid He-4 under microgravity. The crystal remained stuck to the bottom of the sample cell even in the 20 seconds microgravity condition.
  • Satoshi Murakawa, Yuichiro Wada, Yuta Tamura, Masahiro Wasai, Masamichi Saitoh, Yuki Aoki, Ryuji Nomura, Yuichi Okuda, Yasushi Nagato, Mikio Yamamoto, Seiji Higashitani, Katsuhiko Nagai
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (1) 0031-9015 2011/01 [Refereed][Not invited]
     
    The superfluid He-3 B phase, one of the oldest unconventional fermionic condensates experimentally realized, is recently predicted to support Majorana fermion surface states. Majorana fermion, which is characterized by the equivalence of particle and antiparticle, has a linear dispersion relation referred to as the Majorana cone. We measured the transverse acoustic impedance Z of the superfluid He-3 B phase changing its boundary condition and found a growth of peak in Z on a higher specularity wall. Our theoretical analysis indicates that the variation of Z is induced by the formation of the cone-like dispersion relation and thus confirms the important feature of the Majorana fermion in the specular limit.
  • Ryuji Nomura, Satoshi Murakawa, Yuichiro Wada, Yuta Tamura, Masahiro Wasai, Kouki Akiyama, Masamichi Saitoh, Yuki Aoki, Yuichi Okuda
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 43 (3) 718 - 721 1386-9477 2011/01 [Refereed][Not invited]
     
    Surface Andreev bound states of superfluid He-3 have been detected by transverse acoustic impedance measurement. In the diffusive limit of the quasiparticle scattering off a wall, a singularity in the temperature dependence of the acoustic impedance appears at a particular temperature. At this temperature, pair excitations of the surface Andreev bound state quasiparticle and the propagating Bogoliubov quasiparticle drastically change their nature due to a very sharp band edge of the surface Andreev bound states, resulting in the singularity of the acoustic impedance. This temperature dependence was well reproduced by a theory which properly takes into account the surface Andreev bound states. In a partially specular wall boundary condition achieved by coating the wall with thin He-4 layers, the singularity shifted to a higher temperature since the bandwidth became broader as the specularity increased. The coating with He-4 influences only the states in the vicinity of the wall and thus the shift is further evidence that the transverse acoustic impedance senses the surface Andreev bound states. (C) 2010 Elsevier B.V. All rights reserved.
  • Satoshi Murakawa, Akira Yamaguchi, Miho Arai, Masahiro Wasai, Yuki Aoki, Hidehiko Ishimoto, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 158 (1-2) 141 - 146 0022-2291 2010/01 [Not refereed][Not invited]
     
    We measured the complex transverse acoustic impedance in both superfluid He-3 A(1) and A(2) phases. This impedance is sensitive to surface states. In our preliminary results, the temperature dependence of the impedance in the A(1) phase is similar to that in A phase, and the imaginary part shows an anomaly in the A(2) phase. These anomalies occurred at the temperature defined as T-k, which is lower as the frequency gets higher. The similar frequency dependence of T-k in each phase suggests that the anomaly is attributed to the same origin. The frequency dependence of the T-k/T-c indicates that the shape of the surface density of each spin pair state did not greatly change in the present experimental temperature range.
  • Masahiro Wasai, Satoshi Murakawa, Yuta Tamura, Yuichiro ada, Yuki Aoki, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 158 (1-2) 268 - 274 0022-2291 2010/01 [Not refereed][Not invited]
     
    We measured transverse acoustic impedance Z of normal fluid He-3 at 46.6 MHz on a surface coated with a thin He-4 film. The real component of the impedance, Z', in the coated samples deviates from Z' in the pure He-3 in the low temperature region. Z' on the coated samples is almost identical with Z' in the pure sample at high temperature and gradually deviates below a particular temperature T-onset. T-onset is possibly the superfluid onset temperature of the He-4 film pressurized by the bulk liquid He-3. The gradual decrease in Z' means that the superfluid component in He-4 film increases gradually, which is expected from the dynamic KT transition at high frequency. The thicker is the film, the higher is the T-onset. The range of T-onset we observed was between 40 and 160 mK. This is much lower than that at the saturated vapor pressure. Suppression of T-onset achieved by the applied pressure from bulk liquid He was presumably caused by the dissolved He-3 in the film, thickening of the inert layers and/or by the strong correlation effect. The result shows that the specularity of He-3 quasiparticle scattering is strongly affected by superfluidity of the He-4 film.
  • S. Murakawa, Y. Tamura, Y. Wada, M. Wasai, M. Saitoh, Y. Aoki, R. Nomura, Y. Okuda, Y. Nagato, M. Yamamoto, S. Higashitani, K. Nagai
    PHYSICAL REVIEW LETTERS 103 (15) 155301  0031-9007 2009/10 [Not refereed][Not invited]
     
    We measured the transverse acoustic impedance of superfluid He-3-B with a wall coated by several layers of He-4. The coating is known to enhance the specularity in quasiparticle scattering by the wall. We found a new anomaly, a bump and a peak, in the temperature dependence of the transverse acoustic impedance. This agrees with a theoretical calculation using a partially specular wall boundary condition. The new anomaly is shown to arise from a change in the surface density of states by coating and the scattering of thermally occupied surface bound states to other states. The change is towards the density of states of Majorana cone in the specular limit.
  • H. Abe, M. Morikawa, T. Ueda, R. Nomura, Y. Okuda, S. N. Burmistrov
    JOURNAL OF FLUID MECHANICS 619 261 - 275 0022-1120 2009/01 [Not refereed][Not invited]
     
    In order to compare the bubble dynamics of various quantum liquids, we performed the visual observation of a sound-induced bubble in a normal liquid He-4, pure superfluid He-4, and superfluid He-3 He-4 liquid mixtures of saturated and unsaturated He-3 concentrations. When all acoustic wave pulse was applied to these liquids under saturated vapour pressure, a macroscopic bubble was generated on the surface of a piezoelectric transducer. For all liquids, the size of the bubble increased, as a higher voltage was applied to the transducer at a fixed temperature. In the normal He-4 we observed a primary bubble surrounded with many small bubbles which ascended upward together. In contrast to normal phase, only one bubble was generated in the superfluid He-4, and its shape proved to be highly irregular with an ill-defined surface. In the He-3 saturated superfluid mixture, we also observed a solitary bubble but with a nearly perfect spherical shape. The bubble in this mixture expanded on the transducer surface, grew to a maximum size of the order of 1 mm and then started shrinking. As the bubble detached from the transducer with shrinking, we clearly detected an origination of the upward jet flow which penetrated the bubble. The jet velocity in the liquid mixture was approximately 10(2) 10(3) times smaller than in water. At the final stage of the process we could sometimes observe a vortex ring generation. It is interesting that, though the bubble size and time scale of the phenomenon differ from those in water, the behaviour in the collapsing process had much in common with the simulation study of the vortex ring generation in water. In addition, for the mixture with the unsaturated He-3 concentration of about 25% at 600 mK, the shape of the upward jet was observed distinctly, using more precise measurement with shadowgraph method.
  • M. Morikawa, H. Abe, R. Nomura, Y. Okuda
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 032064  1742-6588 2009 [Not refereed][Not invited]
     
    We were able to nucleate as gas bubble in the diluted phase of He-3-He-4 mixture by a 1 ms width strong sound pulse. The nucleated bubble became large and detached from the bottom transducer and was pushed out to the bulk liquid by the acoustic wave pulse. The bubble then repeatedly expanded and contracted a few times and finally disappeared. The overall motion of the bubble was traced by a high speed camera with a time resolution of 1 ms. We are attempting to investigate the small density fluctuation around the bubble by incorporating holographic interferometry technology. The measurement was done at T=0.35 K for the phase separated mixture at saturated vapor pressure. An acoustic wave transducer was located at the bottom of the cell, so the bubble was nucleated in the dilute phase of the mixture. We resolved the density fluctuation as small as Delta rho/rho = 2 x 10(-6) in the dilute phase with the sample width of 25 mm, which could not be obtained by other methods. It was found that there appeared a less dense region of -Delta rho/rho similar to 1.46 x 10(-3) just above the bubble. The bubble appeared just after the pulse was turned off, but this less dense region appeared prior to the emergence of the bulk bubble. It should be an important information about the bubble nucleation mechanism. This very high sensitivity of holographic interferometry with respect to the density fluctuation could be widely used in quantum liquid.
  • Yuta Tamura, Satoshi Murakawa, Yuichiro Wada, Masahiro Wasai, Masamichi Saitoh, Yuki Aoki, Ryuji Nomura, Yuichi Okuda
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 1742-6588 2009 [Refereed][Not invited]
     
    We measured the transverse acoustic impedance of the normal liquid (3)He at 16 MHz and 10 bar with and without (4)He layers plated on a wall in the temperature range of 500 to 3 mK. The real component of the impedance gradually increased with cooling in the high-temperature hydrodynamic region and saturated in the low-temperature collisionless region. In the crossover region around 20 mK, the real component had a steep increase and the imaginary component was minimum. Overall change in the temperature dependence became smaller by (4)He coating and we can obtain the specularity parameter S of the wall by fitting the temperature dependence of the experimental impedance to the theory.
  • S. Murakawa, Y. Wada, Y. Tamura, M. Saitoh, Y. Aoki, R. Nomura, Y. Okuda, Y. Nagato, M. Yamamoto, S. Higashitani, K. Nagai
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 1742-6588 2009 [Refereed][Not invited]
     
    The surface states in superfluid He-3 were studied by measuring the transverse acoustic impedance. To reveal the boundary condition dependence of the surface state, the surface was coated with He-4. Evidence of modification of the surface density of states was determined from the temperature dependence of transverse acoustic impedance in both superfluid A phase and B phase.
  • Yuichiro Wada, Satoshi Murakawa, Yuta Tamura, Masamichi Saitoh, Yuki Aoki, Ryuji Nomura, Yuichi Okuda
    PHYSICAL REVIEW B 78 (21) 214516  1098-0121 2008/12 [Not refereed][Not invited]
     
    A measurement of the surface Andreev bound states of the superfluid He-3-B phase under different boundary conditions is presented. Transverse-acoustic impedance spectroscopy was used to determine the bandwidth of the bound states on a wall with various specularities. It was found that the band was broader for larger specularity and filled up the superfluid gap above a critical specularity. Specularity was controlled by coating the wall with thin layers of He-4 and was evaluated separately using acoustic impedance measurement in the normal-fluid phase.
  • Yuichi Okuda, Ryuji Nomura
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (11) 111009-1-10  0031-9015 2008/11 [Not refereed][Not invited]
     
    The new aspects of crystal growth in solid He-4 at low temperatures are revealed by manipulating the crystal with a radiation pressure of acoustic waves. The acoustic radiation pressure is generally a tiny nonlinear effect, but it has given unexpected effect on the surface of He-4 owing to the markedly high growth rate of the crystal. Radiation pressure induces crystallization or melting. Owing to the strong temperature dependences of the growth rate of an atomically rough surface, which increases divergingly towards T = 0, and the numerical value of the ratio of the sound velocities in both phases, the crystal melts at high temperatures when the sound wave is applied from the solid side, while it grows at low temperatures under the same conditions. We found a new type of growth mechanism of a c-facet driven by a strong radiation pressure. The growth rate of a c-facet was found to be much higher than the conventional screw-dislocation-mediated mechanism. Theoretical analysis that treated elementary steps as quantum mechanical quasi-particles reproduced the observed important feasures. The superflow around steps was taken into account as the kinetic energy of the steps. Finally, it was demonstrated that the use of radiation pressure enables the creation of negative crystals or superfluid bubbles in the crystal. Various interesting motions and shapes of the negative crystal were observed and interpreted using a simple model.
  • Ryuji Nomura, Aiko Osawa, Tomohiro Mimori, Ken-Ichi Ueno, Haruko Kato, Yuichi Okuda
    PHYSICAL REVIEW LETTERS 101 (17) 175703  0031-9007 2008/10 [Not refereed][Not invited]
     
    The dynamical transition in the crystallization of (4)He in aerogel has been investigated by direct visualization and dynamical phase diagrams have been determined. The crystal-superfluid interface in aerogel advances via creep at high temperatures and avalanches at low temperatures. The transition temperature is higher at a higher interface velocity and lower in higher porosity aerogels. The transition is due to competition between thermal fluctuations and disorder for the crystallization process.
  • Bubble nucleation in a superfluid3He-4He mixture induced by acoustic wave
    H. Abe, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda, S. N. Burmistrov
    Fizika Nizkikh Temperatur (Kharkov) 34 (4-5) 391 - 394 0132-6414 2008/04 
    We report the nucleation dynamics of bubbles induced by an acoustic wave pulse in 3He- 4He liquid mixtures. The experiment was performed for the mixture with 3He fixed concentrations of about 4% and 25% and the pure superfluid 4He. When a pulse of 1 ms duration was applied to the mixture at the saturated vapor pressure, a spherical bubble was nucleated on the active area of a piezoelectric transducer. For the case of pure 4He, not a spherically shaped bubble, but an irregularly shaped, larger one was observed. We took pictures with a high speed CCD camera of the bubble expansion and contraction motions after the nucleation, We also investigated the temperature dependence of the bubble nucleation by changing the acoustic wave power. The results show that the nucleation and growth dynamics of a cavitation bubble depend greatly on the 3He concentration and temperature.
  • H. Abe, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda, S. N. Burmistrov
    LOW TEMPERATURE PHYSICS 34 (4-5) 308 - 311 1063-777X 2008/04 [Not refereed][Not invited]
     
    The nucleation dynamics of bubbles induced by an acoustic wave pulse in He-3-He-4 liquid mixtures is reported. The experiment is performed mixtures with fixed He-3 concentrations of about 4% and 25% and for pure superfluid He-4. When a pulse of 1 ms duration is applied to the mixture at the saturated vapor pressure, a spherical bubble is nucleated on the active area of a piezoelectric transducer. For the case of pure He-4 it is not a spherically shaped bubble but an irregularly shaped, larger one that is observed. Pictures of the bubble expansion and contraction motions after the nucleation are taken with a high speed CCD camera. The temperature dependence of the bubble nucleation is also investigated by changing the acoustic wave power. The results show that the nucleation and growth dynamics of a cavitation bubble depend greatly on the He-3 concentration and temperature. (C) 2008 American Institute of Physics.
  • H. Abe, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda, S. N. Burmistrov
    LOW TEMPERATURE PHYSICS 34 (4-5) 308 - 311 1063-777X 2008/04 [Refereed][Not invited]
     
    The nucleation dynamics of bubbles induced by an acoustic wave pulse in He-3-He-4 liquid mixtures is reported. The experiment is performed mixtures with fixed He-3 concentrations of about 4% and 25% and for pure superfluid He-4. When a pulse of 1 ms duration is applied to the mixture at the saturated vapor pressure, a spherical bubble is nucleated on the active area of a piezoelectric transducer. For the case of pure He-4 it is not a spherically shaped bubble but an irregularly shaped, larger one that is observed. Pictures of the bubble expansion and contraction motions after the nucleation are taken with a high speed CCD camera. The temperature dependence of the bubble nucleation is also investigated by changing the acoustic wave power. The results show that the nucleation and growth dynamics of a cavitation bubble depend greatly on the He-3 concentration and temperature. (C) 2008 American Institute of Physics.
  • Satoshi Murakawa, Yuichiro Wada, Yuta Tamura, Masamichi Saitoh, Yuki Aoki, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 150 (3-4) 154 - 159 0022-2291 2008/02 [Refereed][Not invited]
     
    We measured the complex transverse acoustic impedance of superfluid He-3 in the B phase by coating a surface with He-4 to study the boundary condition dependence of the surface bound states. Observed features in the temperature dependence were similar to those without He-4 coating. However, temperatures showing singularities became higher and variations in the dependence became smaller. The small variations indicated that a specular surface was realized by the He-4 coating. Increase in the singularity temperature indicated that the bandwidth of the surface Andreev bound states became broader by the coating.
  • H. Abe, M. Morikawa, T. Ueda, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 150 (3-4) 289 - 294 0022-2291 2008/02 [Refereed][Not invited]
     
    We report an instability of He-4 crystal surface during a large modification of its shape observed by schlieren photography. He-4 crystal was nucleated on an ultrasound transducer which was placed in the upper part of the sample cell facing the bottom. The crystal was grown on the transducer and the lowest part of it eventually touched the bottom of the cell. Almost immediately, the crystal started to change shape very quickly to adjust itself to the new boundary condition. During this large deformation, the hexagonal shape of the crystal surrounded by facets became unstable and the surface became corrugated. The corrugation pattern during the deformation was observed by a high-speed camera. The results were compared with Kelvin-Helmholtz type instability which Uwaha and Nozieres predicted.
  • Aiko Osawa, Haruko Kato, Tomohiro Mimori, Ryuji Nomura, Yuichi Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 150 (3-4) 499 - 504 0022-2291 2008/02 [Refereed][Not invited]
     
    Static behaviors of crystallization of He-4 in porous materials, such as the increase of melting pressure, have been studied extensively, but nonequilibrium dynamics of the phase transition is hardly known. Our interest was in how He-4 crystals grow in a 90.4% porosity aerogel. Aerogels are transparent and the dynamics in them can be studied visually. A Pomeranchuk-type variable-volume cell was used to study crystallization at a fixed temperature with a blocked capillary condition. By continuously compressing a chamber, the pressure rose above the bulk melting pressure and at a pressure 1.7 bar above the bulk melting pressure these crystals began to invade the aerogel. A clear crystal-superfluid interface was moved smoothly by the steady compression. No macroscopic facets were observed in the aerogel well below the bulk roughening transition temperature.
  • Takao Mizusaki, Ryuji Nomura, Masahiko Hiroi
    JOURNAL OF LOW TEMPERATURE PHYSICS 149 (3-4) 143 - 150 0022-2291 2007/11 [Not refereed][Not invited]
     
    Frost heave phenomena have been studied in He-4 on porous vycor glass, in which He-4 in the pores remained supercooled fluid below the bulk melting temperature, T (m) . When we cool a bulk solid at T below T (m) on the vycor, the bulk solid sucks the supercooled liquid in the pores and grows. We measured the maximum frost heave pressure over bulk melting pressure, P (m) , as a function of Delta T=T (m) -T. When temperature was suddenly lowered, the frost heave pressure increased in time to a next equilibrium pressure and we measured the time constant and derived the frost heave rate. The frost heave rate was measured as a function of temperature and decreased very rapidly as temperature was lowered. We propose models to explain the mass transport in solid either by vacancy or by amorphous solid between bulk solid He-4 and vycor. From measured temperature dependence of the rate in comparison with our model, we conclude the frost heave rate is determined by mass flow in solid He-4 due to thermally-activated vacancy diffusion.
  • Haruka Abe, Tetsuto Ueda, Michihiro Morikawa, Yu Saitoh, Ryuji Nomura, Yuichi Okuda
    PHYSICAL REVIEW E 76 (4) 1539-3755 2007/10 [Refereed][Not invited]
     
    We observed that Faraday waves are parametrically generated on a free surface of superfluid (4)He when a sample cell is vibrated vertically. Standing-wave patterns appear on the surface, and their frequencies are one-half the driving frequency. We observed clear threshold amplitudes of the vibration for the instability. The difference in the threshold between the superfluid and the normal fluid is explained by a wall damping.
  • T. Ueda, H. Abe, Y. Saitoh, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 148 (5-6) 553 - 557 0022-2291 2007/09 [Not refereed][Not invited]
     
    We observed that the Faraday waves were parametrically generated on a free surface of superfluid He-4. Our sample cell was supported by plate springs and had a permanent magnet on the top. It was oscillated by applying oscillating current to a superconducting coil. We prepared the sample cell made of polycarbonate so as to optically observe the superfluid surface. Standing wave patterns appeared on the surface and their frequencies were one half of a driving frequency. We observed clear threshold amplitude of the oscillation for the instability. Threshold is usually determined by the viscosity of fluid and thus there must be a dissipation mechanism in superfluid for the threshold.
  • H. Kato, W. Miyashita, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 148 (5-6) 621 - 625 0022-2291 2007/09 [Not refereed][Not invited]
     
    Silica aerogels are highly porous and very compressible materials. They are transparent and suitable for observation of the liquefaction process in them. We reported that capillary condensation of He-4 in a very light aerogel with a porosity of 99.5% proceeded with two steps under a nonequilibrium condition. The aerogel sucked outer liquid with two separated interfaces which were regarded as precursor films and avalanches (Nomura, R., et al. in Phys. Rev. E 73:032601, 2006). During the capillary condensation, shrinkage of the aerogel was large enough to be visually observable, shrinking about 1.5% in length by the capillary force. During the rapid evacuation at high temperatures, shrinkage was enhanced to as much as 7% and was easily seen. By repeated filling and evacuating of the liquid in the aerogel, the shrinkage became less. For denser aerogels with porosities of 95.8 and 90.4%, the shrinkage was not large enough to be observed by our method.
  • R. Nishida, J. Taniguchi, R. Nomura, Y. Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 148 (3-4) 109 - 113 0022-2291 2007/08 [Not refereed][Not invited]
     
    We observed a profile of nonequilibrium superfluid-normal (SN) interface of He-4 near a vertical wall. A glass, brass or copper wall was used. The SN interface was produced by cooling liquid He-4 in a bath from the bottom, where liquid He-4 was pumped through a flow impedance in order to cool down the liquid. Superfluid (Normal fluid) occupied the lower (upper) part of the bath. The SN interface was visualized by three methods: simple visualization, shadowgraphy and schlieren method. The interface touched a vertical glass wall at almost 90 degrees. A large hollow was observed near a brass wall which had intermediate thermal conductivity. Downward flow was observed on a copper wall due to the very good thermal conductivity of the wall. Various types of interface profile were observed depending on the thermal conductivity of the wall used.
  • H. Abe, T. Ueda, Y. Saitoh, R. Nomura, Y. Okuda, S. N. Burmistrov
    JOURNAL OF LOW TEMPERATURE PHYSICS 148 (3-4) 133 - 138 0022-2291 2007/08 [Not refereed][Not invited]
     
    We report visual observation of a sound-induced bubble in superfluid He-3-He-4 liquid mixtures using a high-speed camera at a rate of 1 msec/frame. The experiments were performed in the He-3 dilute phase of phase-separated mixtures at 300 mK. The resonant frequency of the piezoelectric transducer was 9.36 MHz and the diameter of the active electrode was about 4 mm. When an acoustic wave pulse of sufficient magnitude was applied to the dilute phase from the transducer under saturated vapor pressure, a single bubble was nucleated on the active area. The bubble expanded almost spherically on the transducer, as it reached maximum size, it started shrinking, detached from the transducer, and collapsed. We also investigated the motion of the bubble in mixtures with a 3He concentration of 25% at 750 mK. In this case, the bubble grew elliptically on the transducer and detached from it without much change in shape.
  • E. B. Gordon, R. Nishida, R. Nomura, Y. Okuda
    JETP LETTERS 85 (11) 581 - 584 0021-3640 2007/08 [Refereed][Not invited]
     
    The hydrogen molecules embedded in superfluid helium as a gas jet are shown to form long thin filaments. These filaments survived under a helium transition to anormal phase demonstrating their conjugated entity. The concentration of an impurity in the core of the vortex may be the mechanism of the impurity coalescence providing a cotton-like structure of the condensate obtained by introducing an impurity-containing gas helium jet to He-II.
  • Haruka Abe, Tetsuto Ueda, Michihiro Morikawa, Yu Saitoh, Ryuji Nomura, Yuichi Okuda
    12TH INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER (PHONONS 2007) 92 1742-6588 2007 [Refereed][Not invited]
     
    Periodic modulation of the gravity acceleration makes a flat surface of a fluid unstable and standing waves are parametrically excited on the surface. This phenomenon is called Faraday instability. Since a crystal-superfluid interface of (4)He at low temperatures is very mobile and behaves like a fluid surface, Saarloos and Weeks predicted that Faraday instability of the crystallization waves exists in (4)He and that the threshold excitation for the instability depends on the crystal growth coefficient. We successfully observed the Faraday instability of the crystal-liquid interface at 160 mK. Faraday waves were parametrically generated at one half of the driving frequency 90 Hz. Amplitude of the Faraday wave becomes smaller at higher temperature due to decrease of the crystal growth coefficient and disappears above 200 mK.
  • Masamichi Saitoh, Yuichiro Wada, Yuki Aoki, Satoshi Murakawa, Ryuji Nomura, Yuichi Okuda
    PHYSICAL REVIEW B 74 (22) 1098-0121 2006/12 [Refereed][Not invited]
     
    The surface density of states (SDOS) in superfluid (3)He at a diffusive wall was investigated by systematic measurements of the transverse acoustic impedance Z. The observed difference between the temperature dependence of Z in the A and B phases can be explained by a difference in the SDOS of each phase. In the B phase, an additional gap in the SDOS opened between the upper energy edge Delta(*) of the surface Andreev bound states band and the bulk energy gap Delta. The temperature dependence of Delta(*) was measured and was about 30% smaller than the theoretical value. In the A phase, a flat and gapless SDOS was confirmed experimentally.
  • R Nomura, K Yoneyama, Y Okuda
    PHYSICAL REVIEW E 73 (4) 049901  1539-3755 2006/04 [Not refereed][Not invited]
  • R Nomura, K Yoneyama, Y Okuda
    PHYSICAL REVIEW E 73 (4) 1539-3755 2006/04 [Refereed][Not invited]
  • R Nomura, W Miyashita, K Yoneyama, Y Okuda
    PHYSICAL REVIEW E 73 (3) 032601  1539-3755 2006/03 [Not refereed][Not invited]
     
    Dynamics of capillary condensation of liquid He-4 in various density silica aerogels was investigated systematically. Interfaces were clearly visible when bulk liquid was rapidly sucked into the aerogel. Time evolution of the interface positions was consistent with the Washburn model and their effective pore radii were obtained. Condensation was a single step in a dense aerogel and two steps in a low density aerogel. Crossover between the two types of condensation was observed in an intermediate density aerogel. Variety of the dynamics may be the manifestation of the fractal nature of aerogels which had a wide range of distribution of pore radii.
  • H Abe, Y Saitoh, T Ueda, F Ogasawara, R Nomura, Y Okuda, AY Parshin
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (2) 023601-1-4  0031-9015 2006/02 [Not refereed][Not invited]
     
    Very fast growth of the c-facet of a He-4 crystal was induced by acoustic waves. The growth velocity was larger at lower temperatures and saturated below about 400 mK. The velocity was proportional to the acoustic wave power. This fast growth cannot be explained by the spiral growth mechanism for the known value of the step mobility. We developed a step multiplication model for high-power acoustic waves and found reasonable agreement with the observed temperature and power dependence of the growth velocity.
  • W. Miyashita, K. Yoneyama, H. Kato, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 251 - + 0094-243X 2006 [Not refereed][Not invited]
     
    Capillary condensation of liquid He-4 in silica aerogel with a 90% porosity was investigated visually. The initial condition of the experiment was such that liquid He-4 was present in the sample cell but not in the aerogel. This situation was realized by introducing the liquid into the cell at a fast rate to avoid liquefaction in the aerogel. The free surface of the liquid rose up in the cell with filling and eventually reached the bottom of the aerogel. Then, the aerogel absorbed the liquid by capillary condensation. The height of the liquid in the aerogel rose with time t roughly as t(1/2) in the normal fluid phase. This behavior was consistent with the Washburn model. When the system was cooled through the lambda point during the condensation, the liquid height started to rise faster in the superfluid phase with a constant velocity of about 0.3 mm/sec. The dynamics of capillary condensation was strongly dependent on whether the liquid He-4 was in the normal or the superfluid phase.
  • M. Saitoh, Y. Wada, Y. Aoki, R. Nishida, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 89 - + 0094-243X 2006 [Not refereed][Not invited]
     
    By using an AC-cut quartz transducer at the frequencies of 9.56 and 28.7 MHz, we observed discontinuity in the temperature dependence of transverse acoustic impedance of superfluid He-3 at 24.9 bar. Though the transverse acoustic response of superfluid He-3 is not well understood, we can conclude that the discontinuity occurred at the A-B transition, from its temperature and frequency dependence. Since the density of states near the boundary within a coherence length dominates the momentum transfer between an oscillating wall and He-3 quasi-particles, the large difference in the transverse acoustic impedance between the A and B phases can be explained by a difference in the symmetry of the order parameters near the wall.
  • Y. Wada, Y. Aoki, M. Saitoh, R. Nishida, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 91 - + 0094-243X 2006 [Not refereed][Not invited]
     
    We measured the pressure dependence of the complex transverse acoustic impedance of superfluid 3 He-B using an AC-cut quartz transducer. The measurements were performed by a CW bridge method at the third harmonics of the fundamental resonance frequency 9.56 MHz. We obtained the real (Z') and the imaginary (Z") parts of the transverse acoustic impedance independently. Z' and Z" did not change from the normal state values at T-c but Z' started to increase at the pair breaking edge temperature T-pb upon cooling. The slope of the increase changed at a temperature defined as T* which was lower than T-pb. With further cooling, it reached a maximum and then decreased slowly. Z" had a small peak at T* and decreased rapidly with decreasing temperature. These temperature dependences were possibly influenced by quasi-particle density of states within the energy gap originating from the surface Andreev bound states. At lower pressure the maximum of Z' and the small peak of Z" moved to smaller T/T-c and became larger due to the pressure dependence of the energy gap.
  • H. Abe, F. Ogasawara, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 145 - + 0094-243X 2006 [Not refereed][Not invited]
     
    We report the first study of a bubble nucleation in the dilute He-3 phase of phase-separated He-3-He-4 liquid mixtures. When an acoustic wave pulse of 1 msec duration was applied to the dilute phase at saturated vapor pressure, a single bubble was nucleated on an active area of the piezoelectric transducer. We succeeded in observing fast motion of the bubble by using a high-speed camera. We also observed bubbles nucleated in the 3 He rich phase and the pure superfluid He-4 by acoustic waves. Bubble shape in the dilute He-3 phase was similar to that in He-3 rich phase but quite different from that in pure superfluid He-4.
  • Y. Saitoh, T. Ueda, F. Ogasawara, H. Abe, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 345 - + 0094-243X 2006 [Not refereed][Not invited]
     
    Displacement of the solid-liquid interface of He-4 induced by a heat pulse of 2 ms duration was measured by a high-speed camera. Either crystallization or melting was induced at low temperatures depending on whether the heat pulse was applied to the interface from the solid side or the liquid side. The heat pulse had qualitatively the same effect on the interface as acoustic waves reported in R. Nomura et al., Phys. Rev. B 70 054516 (2004). However, the effect was smaller and a larger power was needed to induce an interface motion than acoustic waves. Another difference between them is that the heat pulse induced no interface motion at all above 0.8 K, where acoustic waves induced melting.
  • J. Taniguchi, R. Nishida, A. Ogino, R. Nomura, Y. Okuda
    J. Jpn. Soc. Microgravity Appl. 日本マイクログラビティ応用学会 23 (3) 134 - 138 0915-3616 2006 [Not refereed][Not invited]
  • W. Miyashita, K. Yoneyama, H. Kato, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 251 - + 0094-243X 2006 [Refereed][Not invited]
     
    Capillary condensation of liquid He-4 in silica aerogel with a 90% porosity was investigated visually. The initial condition of the experiment was such that liquid He-4 was present in the sample cell but not in the aerogel. This situation was realized by introducing the liquid into the cell at a fast rate to avoid liquefaction in the aerogel. The free surface of the liquid rose up in the cell with filling and eventually reached the bottom of the aerogel. Then, the aerogel absorbed the liquid by capillary condensation. The height of the liquid in the aerogel rose with time t roughly as t(1/2) in the normal fluid phase. This behavior was consistent with the Washburn model. When the system was cooled through the lambda point during the condensation, the liquid height started to rise faster in the superfluid phase with a constant velocity of about 0.3 mm/sec. The dynamics of capillary condensation was strongly dependent on whether the liquid He-4 was in the normal or the superfluid phase.
  • H. Abe, F. Ogasawara, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 145 - + 0094-243X 2006 [Refereed][Not invited]
     
    We report the first study of a bubble nucleation in the dilute He-3 phase of phase-separated He-3-He-4 liquid mixtures. When an acoustic wave pulse of 1 msec duration was applied to the dilute phase at saturated vapor pressure, a single bubble was nucleated on an active area of the piezoelectric transducer. We succeeded in observing fast motion of the bubble by using a high-speed camera. We also observed bubbles nucleated in the 3 He rich phase and the pure superfluid He-4 by acoustic waves. Bubble shape in the dilute He-3 phase was similar to that in He-3 rich phase but quite different from that in pure superfluid He-4.
  • Y. Saitoh, T. Ueda, F. Ogasawara, H. Abe, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 345 - + 0094-243X 2006 [Refereed][Not invited]
     
    Displacement of the solid-liquid interface of He-4 induced by a heat pulse of 2 ms duration was measured by a high-speed camera. Either crystallization or melting was induced at low temperatures depending on whether the heat pulse was applied to the interface from the solid side or the liquid side. The heat pulse had qualitatively the same effect on the interface as acoustic waves reported in R. Nomura et al., Phys. Rev. B 70 054516 (2004). However, the effect was smaller and a larger power was needed to induce an interface motion than acoustic waves. Another difference between them is that the heat pulse induced no interface motion at all above 0.8 K, where acoustic waves induced melting.
  • Y. Wada, Y. Aoki, M. Saitoh, R. Nishida, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 91 - + 0094-243X 2006 [Refereed][Not invited]
     
    We measured the pressure dependence of the complex transverse acoustic impedance of superfluid 3 He-B using an AC-cut quartz transducer. The measurements were performed by a CW bridge method at the third harmonics of the fundamental resonance frequency 9.56 MHz. We obtained the real (Z') and the imaginary (Z") parts of the transverse acoustic impedance independently. Z' and Z" did not change from the normal state values at T-c but Z' started to increase at the pair breaking edge temperature T-pb upon cooling. The slope of the increase changed at a temperature defined as T* which was lower than T-pb. With further cooling, it reached a maximum and then decreased slowly. Z" had a small peak at T* and decreased rapidly with decreasing temperature. These temperature dependences were possibly influenced by quasi-particle density of states within the energy gap originating from the surface Andreev bound states. At lower pressure the maximum of Z' and the small peak of Z" moved to smaller T/T-c and became larger due to the pressure dependence of the energy gap.
  • M. Saitoh, Y. Wada, Y. Aoki, R. Nishida, R. Nomura, Y. Okuda
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 89 - + 0094-243X 2006 [Refereed][Not invited]
     
    By using an AC-cut quartz transducer at the frequencies of 9.56 and 28.7 MHz, we observed discontinuity in the temperature dependence of transverse acoustic impedance of superfluid He-3 at 24.9 bar. Though the transverse acoustic response of superfluid He-3 is not well understood, we can conclude that the discontinuity occurred at the A-B transition, from its temperature and frequency dependence. Since the density of states near the boundary within a coherence length dominates the momentum transfer between an oscillating wall and He-3 quasi-particles, the large difference in the transverse acoustic impedance between the A and B phases can be explained by a difference in the symmetry of the order parameters near the wall.
  • W Miyashita, K Yoneyama, R Nomura, Y Okuda
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 (8-9) 1509 - 1511 0022-3697 2005/08 [Not refereed][Not invited]
     
    Liquefaction dynamics of He-4 in a silica aerogel with porosity of 90% was studied optically at 2.4 K. At low condensation rate of gas into a sample cell the aerogel became opaque during the condensation and then finally cleared up. Liquid outside of the aerogel appeared after the liquefaction in the aerogel was completed. At high condensation rate liquid appeared outside of the aerogel first and filled the lower part of the sample cell. When the surface of the liquid reached the bottom of the aerogel, the aerogel sucked up the liquid and made a visible interface in the aerogel. The height of the interface was proportional to the square root of time. This behaviour was consistent with the Washburn model and the effective pore radius obtained was 9.4 nm. (c) 2005 Elsevier Ltd. All rights reserved.
  • Y Aoki, Y Wada, M Saitoh, R Nomura, Y Okuda
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 (8-9) 1349 - 1351 0022-3697 2005/08 [Not refereed][Not invited]
     
    Transverse acoustic response in the B-phase of superfluid 3 He was measured by using an AC-cut quartz transducer at a pressure of 17.0 bar. The measurements were performed by a CW bridge method at a frequency of about 9.6 MHz utilizing a quadrature hybrid and a high-frequency lock-in amplifier. By sweeping frequency around the resonance frequency of the transducer, in-phase and quadrature responses of the resonance were obtained from the output of the high-frequency lock-in amplifier. The change of the Delta Q(-1) and the resonance frequency Delta fo which were proportional to the real and the imaginary part of the transverse acoustic impedance of superfluid 3 He were obtained separately. (c) 2005 Elsevier Ltd. All rights reserved.
  • R Nomura, F Ogasawara, Y Saitoh, H Abe, Y Okuda
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 (8-9) 1467 - 1470 0022-3697 2005/08 [Not refereed][Not invited]
     
    interface motions of He-4 crystals induced by acoustic waves were investigated in various surface orientations. Inversion of a direction of the force on the interface was observed in the case of acoustic wave from the crystal side above a particular temperature T-i.T-i was about 0.8 K in rough surface and decreased to 0.6 K with approaching the c-facet. These observations were qualitatively explained assuming that the interface motion was induced by acoustic radiation pressure. Relaxation of the interface after stopping the acoustic wave was observed by a high-speed video camera. (c) 2005 Elsevier Ltd. All rights reserved.
  • Y Aoki, Y Wada, M Saitoh, R Nomura, Y Okuda, Y Nagato, M Yamamoto, S Higashitani, K Nagai
    PHYSICAL REVIEW LETTERS 95 (7) 075301  0031-9007 2005/08 [Not refereed][Not invited]
     
    Complex transverse acoustic impedance of the superfluid He-3-B was measured at the frequencies of 10 to 80 MHz at 17.0 bar by a cw bridge method. The observed temperature dependence was well explained by the quasiclassical theory with random S-matrix model for a diffusive surface. The temperature dependence was influenced by pair breaking and by quasiparticle density of states at the surface, which was drastically modified from the bulk one by the presence of surface Andreev bound states.
  • H Abe, F Ogasawara, Y Saitoh, T Tatara, S Kimura, R Nomura, Y Okuda
    PHYSICAL REVIEW B 71 (21) 214506-1-7  1098-0121 2005/06 [Not refereed][Not invited]
     
    We demonstrated that acoustic waves could induce nucleation of both a He-4 crystal in superfluid and a superfluid droplet in the crystal in the same temperature range depending on whether an acoustic transducer was covered by the superfluid or the crystal. The temperature dependences of crystal nucleation at and above the melting pressure and that of superfluid droplet nucleation at the melting pressure were investigated systematically by changing the acoustic wave powers. The nucleation processes were monitored by a high-speed camera. Crystals were nucleated above the melting pressure in a metastable superfluid when the sum of the overpressure and the effective overpressure by the acoustic wave reached a threshold value. Crystal nucleation above the melting pressure was effectively induced by acoustic waves at low temperatures and was not induced at all above 800 mK. Crystal nucleation at the melting pressure was induced when the acoustic wave power exceeded a threshold value. The threshold was temperature independent below 300 mK and increased divergently approaching 600 mK. We saw no sign of nucleation above 600 mK even in our maximum acoustic wave power. Superfluid droplet nucleation at the melting pressure was also induced above a threshold power. The threshold was temperature independent at low temperatures with a small maximum at 600 mK and decreased with warming at high temperatures. All the behaviors cannot be explained by mere heating, and a possible effect of acoustic radiation pressure on the nucleation is discussed.
  • H Abe, F Ogasawara, S Kimura, T Tatara, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 138 (3-4) 835 - 840 0022-2291 2005/02 [Not refereed][Not invited]
     
    When an acoustic wave pulse of several msec was applied to superfluid He-4 at melting pressure, He-4 crystal was nucleated on the transducer and rapidly disappeared after the pulse. We measured thresholds of the acoustic wave power which induced a nucleation in the temperature range between 0.09 K and 1 K. The threshold of the nucleation exhibited no temperature dependence below 0.3 K. The nucleation was not induced above 0.6 K even if the injected acoustic pulse was strong. 0.6 K is close to the inversion temperature at which the direction of the force by acoustic wave was inverted on the solid-liquid interface of He-4 [Phys. Rev. Lett. 90, 075301(2003)]. Our observation indicates that the effect of acoustic radiation pressure contributes to the heterogeneous nucleation by acoustic waves.
  • Y Aoki, Y Wada, A Ogino, M Saitoh, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 138 (3-4) 783 - 788 0022-2291 2005/02 [Refereed][Not invited]
     
    The transverse acoustic response in the B phase of superfluid He-3 has been measured using an AC-cut quartz transducer at a pressure of 17.0 bar. The measurements were performed by a CW bridge method at a frequency of 9.3 MHz utilizing a quadrature hybrid and a high-frequency lock-in amplifier. By sweeping frequency around the resonance frequency of the transducer, in-phase and quadrature responses of the resonance were obtained from the output of the lock-in amplifier. We successfully separated the quality factor and the resonance frequency. Quality factor of the transducer had a small dip just below T-c and increased as rho(n) by cooling, while its resonance frequency decreased sharply at T-c and gradually recovered to the normal state value in the low temperature limit.
  • M Saitoh, Y Aoki, Y Wada, A Ogino, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 138 (3-4) 893 - 898 0022-2291 2005/02 [Refereed][Not invited]
     
    We have developed a new technique to study the transverse acoustic properties of superfluid He-3, by employing a shear horizontal surface acoustic wave (SH-SAW) sensor. The transverse acoustic impedance can be obtained from the velocity and damping of SH-SAW which acoustically couples with liquid He-3 at the interface. Since ultrasonic measurements provide the information about superfluid order-parameter through the excitation of collective modes, the SH-SAW sensor is expected to be a useful tool to study the boundary effect of superfluid He-3. Preliminary measurements were carried out at pressures of 17 and 23 bar, by the pulse transmission method at a frequency of 70 MHz. At 17 bar, imaginary squashing mode was observed as the sharp drop of the imaginary part of acoustic impedance. At 23 bar, the supercooled A-B phase transition was observed, as a jump of the real part of acoustic impedance, which was not observed in the warming process.
  • R. Nomura, S. Kimura, F. Ogasawara, H. Abe, Y. Okuda
    Physical Review B - Condensed Matter and Materials Physics 70 (5) 1 - 54516 0163-1829 2004/08 [Refereed][Not invited]
     
    The interface motion of a He crystal induced by an acoustic wave was investigated. When an acoustic wave was applied from the liquid side, it induced melting of the crystal. When applied from the crystal side, melting was induced at high temperatures and crystallization was induced at low temperatures [Nomura et al., Phys. Rev. Lett. 90, 075301 (2003)]. This means that the direction of the force on the interface was inverted at an inversion temperature Ti. The displacement induced by an acoustic wave pulse was systematically studied in crystals with different surface orientations and it was found that Ti decreased when approaching the c facet. The observed interface motion was analyzed by assuming that it was induced by the acoustic radiation pressure.
  • R Nomura, S Kimura, F Ogasawara, H Abe, Y Okuda
    PHYSICAL REVIEW B 70 (5) 054516-1-7  1098-0121 2004/08 [Not refereed][Not invited]
     
    The interface motion of a He-4 crystal induced by an acoustic wave was investigated. When an acoustic wave was applied from the liquid side, it induced melting of the crystal. When applied from the crystal side, melting was induced at high temperatures and crystallization was induced at low temperatures [ Nomura , Phys. Rev. Lett. 90, 075301 (2003) ]. This means that the direction of the force on the interface was inverted at an inversion temperature T-i. The displacement induced by an acoustic wave pulse was systematically studied in crystals with different surface orientations and it was found that T-i decreased when approaching the c facet. The observed interface motion was analyzed by assuming that it was induced by the acoustic radiation pressure.
  • K Yoneyama, R Nomura, Y Okuda
    PHYSICAL REVIEW E 70 (2) 021606  1539-3755 2004/08 [Not refereed][Not invited]
     
    Superfluid bubbles in a He-4 quantum crystal, which we refer to as quantum negative crystals, were investigated in bcc and hcp phases by visualizing their forms and motions at various temperatures. They were nearly spherical in bcc phase and faceted on the c-plane in their upper part in hcp phase. They steadily rose in the crystal due to gravity. Their direction was vertical in bcc phase and obliquely parallel to the c-facet in hcp phase. We also observed a slowing down of negative crystal in hcp phase caused by the appearance of the a-facet when temperature was lowered. Dynamics and morphology became successively anisotropic with cooling. The driving force by gravity for this motion was derived in the spherical case. Growth coefficient obtained by this model agreed well with the reported values.
  • Y Aoki, Y Wada, Y Sekimoto, W Yamaguchi, A Ogino, M Saitoh, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 134 (3-4) 945 - 958 0022-2291 2004/02 [Refereed][Not invited]
     
    A surface acoustic wave (SAW) sensor can be used to determine the acoustic properties of liquid He. We applied this sensor for liquid He-3 and liquid He-4. Two kinds of SAW were used in this experiment, Rayleigh-SAW and shear horizontal SAW. The damping of Rayleigh-SAW was measured in liquid He-4. The results agreed well with the reported values of the acoustic impedance, and the superfluid transition was clearly seen. The damping and the phase shift of shear horizontal SAW were measured in the normal liquid He-3. Temperature dependence of the damping and the phase shift was analyzed by the viscoelastic model, and the results were compared with the transverse acoustic impedance in the normal He-3.
  • Physics of Quantum Solid in Microgravity
    Y. Okuda, R. Nomura
    J. Jpn. Soc. Microgravity Appl. 22 159 - 164 2004
  • K. Yoneyama, R. Nomura, Y. Okuda
    Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 70 (2) 5  1063-651X 2004 [Refereed][Not invited]
     
    Superfluid bubbles in a [formula presented] quantum crystal, which we refer to as quantum negative crystals, were investigated in bcc and hcp phases by visualizing their forms and motions at various temperatures. They were nearly spherical in bcc phase and faceted on the [Formula presented]-plane in their upper part in hcp phase. They steadily rose in the crystal due to gravity. Their direction was vertical in bcc phase and obliquely parallel to the [Formula presented]-facet in hcp phase. We also observed a slowing down of negative crystal in hcp phase caused by the appearance of the [Formula presented]-facet when temperature was lowered. Dynamics and morphology became successively anisotropic with cooling. The driving force by gravity for this motion was derived in the spherical case. Growth coefficient obtained by this model agreed well with the reported values. © 2004 The American Physical Society.
  • F. Ogasawara, H. Abe, Y. Saitoh, T. Tatara, S. Kimura, R. Nomura, Y. Okuda
    Physica Status Solidi C: Conferences 1 (11) 3003 - 3006 1610-1634 2004 [Refereed][Not invited]
     
    Both nucleation of a 4He crystal in superfluid and that of a 4He superfluid droplet in crystal were found to be induced by a heat pulse at the melting pressure. The time evolutions of nucleation on a heater were directly recorded by a high-speed camera. Duration of the heat pulse was usually 2 msec in this report. The nucleated crystal grew with facets for 4 msec and melted with an irregular shape in 40 msec at 500 mK. The nucleated superfluid droplet in crystal also grew with facets, which was a so-called negative crystal, and disappeared in 10 msec. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S Kimura, F Ogasawara, Y Suzuki, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 134 (1-2) 157 - 162 0022-2291 2004/01 [Not refereed][Not invited]
     
    When acoustic waves were applied to the solid-liquid interface of He-4 perpendicularly from the solid side, the solid was melted at high temperatures and grown at low temperatures. This means that the direction of the force on the interface was inverted at an inversion temperature, T-i. We attributed this effect to the acoustic radiation pressure, which induced crystallization and melting [Phys. Rev. Lett. 90, 075301, (2003)]. Temperature dependence of the interface motion by acoustic waves was investigated in several surface orientations. Anisotropy of T-i was found and T-i was lower on a vicinal surface than on a rough surface.
  • S Kimura, F Ogasawara, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 134 (1-2) 145 - 150 0022-2291 2004/01 [Not refereed][Not invited]
     
    When an acoustic wave pulse was applied to metastable superfluid He-4 above the melting pressure, a bulk He-4 crystal was nucleated in the superfluid at low temperatures. Overpressure in which the metastable liquid could exist was investigated by changing the acoustic wave power. A larger power pulse could nucleate the crystal in smaller overpressures, which decreased linearly in the acoustic wave power.
  • F Ogasawara, H Abe, Y Saitoh, T Tatara, S Kimura, R Nomura, Y Okuda
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL. 1, NO. 11 1 (11) 3003 - 3006 1862-6351 2004 [Not refereed][Not invited]
     
    Both nucleation of a He-4 crystal in superfluid and that of a He-4 superfluid droplet in crystal were found to be induced by a heat pulse at the melting pressure. The time evolutions of nucleation on a beater were directly recorded by a high-speed camera. Duration of the heat pulse was usually 2 msec in this report. The nucleated crystal grew with facets for 4 msec and melted with an irregular shape in 40 msec at 500 mK. The nucleated superfluid droplet in crystal also grew with facets, which was a so-called negative crystal, and disappeared in 10 msec. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • S Kimura, F Ogasawara, Y Suzuki, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 134 (1-2) 157 - 162 0022-2291 2004/01 [Refereed][Not invited]
     
    When acoustic waves were applied to the solid-liquid interface of He-4 perpendicularly from the solid side, the solid was melted at high temperatures and grown at low temperatures. This means that the direction of the force on the interface was inverted at an inversion temperature, T-i. We attributed this effect to the acoustic radiation pressure, which induced crystallization and melting [Phys. Rev. Lett. 90, 075301, (2003)]. Temperature dependence of the interface motion by acoustic waves was investigated in several surface orientations. Anisotropy of T-i was found and T-i was lower on a vicinal surface than on a rough surface.
  • S Kimura, F Ogasawara, R Nomura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 134 (1-2) 145 - 150 0022-2291 2004/01 [Refereed][Not invited]
     
    When an acoustic wave pulse was applied to metastable superfluid He-4 above the melting pressure, a bulk He-4 crystal was nucleated in the superfluid at low temperatures. Overpressure in which the metastable liquid could exist was investigated by changing the acoustic wave power. A larger power pulse could nucleate the crystal in smaller overpressures, which decreased linearly in the acoustic wave power.
  • R Nomura, K Yoneyama, F Ogasawara, M Ueno, Y Okuda, A Yamanaka
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 (8) 5205 - 5207 0021-4922 2003/08 [Not refereed][Not invited]
     
    Longitudinal sound velocity in unidirectional hybrid composites or high-strength fiber-reinforced plastics (FRPs) was measured along the fiber axis over a wide temperature range (from 77 K to 420 K). We investigated two kinds of high-strength crystalline polymer fibers, polyethylene (Dyneema) and polybenzobisoxazole (Zylon), which are known to have negative thermal expansion coefficients and high thermal conductivities along the fiber axis. Both FRPs had very high sound velocities of about 9000m/s at low temperatures and their temperature dependences were very strong. Sound velocity monotonically decreased with increasing temperature. The temperature dependence of sound velocity was much stronger in Dyneema-FRP than in Zylon-FRP.
  • R Nomura, K Yoneyama, F Ogasawara, M Ueno, Y Okuda, A Yamanaka
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 (8) 5205 - 5207 0021-4922 2003/08 [Refereed][Not invited]
     
    Longitudinal sound velocity in unidirectional hybrid composites or high-strength fiber-reinforced plastics (FRPs) was measured along the fiber axis over a wide temperature range (from 77 K to 420 K). We investigated two kinds of high-strength crystalline polymer fibers, polyethylene (Dyneema) and polybenzobisoxazole (Zylon), which are known to have negative thermal expansion coefficients and high thermal conductivities along the fiber axis. Both FRPs had very high sound velocities of about 9000m/s at low temperatures and their temperature dependences were very strong. Sound velocity monotonically decreased with increasing temperature. The temperature dependence of sound velocity was much stronger in Dyneema-FRP than in Zylon-FRP.
  • Manipulation of solid-liquid interface of 4He by acoustic radiation pressure
    R. Nomura, Y. Suzuki, S. Kimura, Y. Okuda, S. Burmistrov
    Fizika Nizkikh Temperatur (Kharkov) 29 (6) 663 - 666 0132-6414 2003/06 
    Acoustic radiation pressure is thought to be very useful for solid 4He experiment under the microgravity. We observed that solid-liquid interface of 4He was manipulated by the acoustic wave. We applied the sound pulse perpendicularly to the flat interface between two transducers. The interface moved to the sound direction at low temperatures. We also checked how the interface moved when sound was applied parallel to the interface. Dynamics of the interface during and after the sound pulse were recorded by a high speed CCD camera.
  • R Nomura, Y Suzuki, S Kimura, Y Okuda, S Burmistov
    LOW TEMPERATURE PHYSICS 29 (6) 492 - 494 1063-777X 2003/06 [Not refereed][Not invited]
     
    Acoustic radiation pressure is thought to be very useful for solid He-4 experiments under microgravity. We observed the manipulation of a He-4 solid-liquid interface by an acoustic wave. We applied a sound pulse in a direction perpendicular to the flat interface between two transducers. At low temperatures the interface moved in the sound direction. We also checked how the interface moved when sound was applied parallel to the interface. The interface dynamics during and after the sound pulse were recorded with a high speed CCD camera. (C) 2003 American Institute of Physics.
  • Y Suzuki, S Kimura, M Maekawa, M Ueno, R Nomura, Y Okuda, S Burmistrov
    PHYSICA B-CONDENSED MATTER 329 364 - 365 0921-4526 2003/05 [Not refereed][Not invited]
     
    A solid-liquid interface of He-4 was prepared between two transducers and ultrasound was applied to it perpendicularly. Solid He-4 was grown when the ultrasound was applied to the interface from the solid side and melted from the liquid side at temperatures below 750 mK. Above 750 mK it was melted in both sound directions. This growth and melting is explained qualitatively by the acoustic radiation pressure and the temperature dependent sound transmission coefficients. Using this new way of operating the interface the mobility of the interface was measured in growing and melting cases separately and found to have different values in some crystal orientations. (C) 2003 Elsevier Science B.V. All rights reserved.
  • R Nomura, M Ueno, Y Okuda, S Burmistrov, A Yamanaka
    PHYSICA B-CONDENSED MATTER 329 1664 - 1665 0921-4526 2003/05 [Not refereed][Not invited]
     
    Sound velocities of fiber reinforced plastics (FRPs) were measured along the fiber axis at temperatures between 360 and 77 K. We used two kinds of the high-strength crystalline polymer fibers, polyethylene (Dyneema) and polybenzobisoxazole (Zylon), which have negative thermal expansion coefficients. They also have high thermal conductivities and high resistances for flash over voltage, and are expected as new materials for coil bobbins or spacers at cryogenic temperatures. They have very large sound velocities of about 9000 (m/s) at 77 K, which are 4.5 times larger than that of the ordinary polyethylene fiber. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Aoki, Y Sekimoto, Y Wada, W Yamaguchi, R Nomura, YO Da
    PHYSICA B-CONDENSED MATTER 329 116 - 117 0921-4526 2003/05 [Refereed][Not invited]
     
    We developed a shear horizontal surface acoustic wave (SH-SAW) sensor to investigate the viscoelastic properties and the transverse sound in normal and superfluid He-3. The SAW was generated and detected by two sets of interdigital transducers on LiTaO3 substrate. The distance between generator and detector was 21 nm. The SAW frequency was 69.4 MHz and operated in the pulse mode. In an SH-SAW substrate displacement is transverse to the propagation direction on the substrate surface. It is coupled with the viscosity of the surrounding liquid He-3. Velocity and damping of SH-SAW were measured in normal liquid He-3 down to 14 mK. Temperature dependences of the velocity and the damping were explained well by assuming the viscoelastic properties of normal liquid He-3. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Aoki, W Yamaguchi, Y Wada, Y Sekimoto, R Nomura, Y Okuda
    PHYSICA B-CONDENSED MATTER 329 234 - 235 0921-4526 2003/05 [Refereed][Not invited]
     
    Damping and velocity of Rayleigh surface acoustic waves (SAW) were measured in liquid He-4. A Rayleigh-SAW propagates along the substrate surface by emitting compressional waves into the liquid and thus the damping of the Rayleigh-SAW is determined by the acoustic impedance of the surrounding liquid He-4. Temperature dependence agreed well with the reported values of the impedance and the superfluid transition in He-4 was clearly seen. We also set up a reflection plate 1.5 mm above the SAW device which reflected the emission waves. They were converted back into the SAW and used to, measure the velocity and damping of ultrasound in liquid He-4 separately. (C) 2003 Elsevier Science B.V. All rights reserved.
  • R Nomura, Y Suzuki, S Kimura, Y Okuda
    PHYSICAL REVIEW LETTERS 90 (7) 075301  0031-9007 2003/02 [Not refereed][Not invited]
     
    Crystallization and melting of helium-4 was experimentally observed to be induced by acoustic radiation pressure where the liquid-solid interface is highly mobile at low temperatures. We discuss the observed anomalous reversal of this effect as a function of temperature and the nucleation by acoustic wave pulses of crystals in the liquid phase or liquid bubbles in the solid phase. A high-speed camera was used for the in situ observation of large interface velocities as high as 1 m/sec.
  • Y Okumura, M Maekawa, R Nomura, Y Okuda
    PHYSICA B-CONDENSED MATTER 316 613 - 615 0921-4526 2002/05 [Not refereed][Not invited]
     
    We observed the melting of solid He-4 in a superfluid when sound waves were injected to its rough surface at 1.2 K. A single crystal was grown between two transducers and ultrasound pulses were applied normally to the solid-liquid interface from the solid or liquid side. Amount of melting was on the same order in both cases. We measured the amount of melting precisely by changing the sound power and the number of pulses. We also proposed the possible mechanism of the sound induced melting of solid He-4. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Y Okumura, M Maekawa, Y Suzuki, R Nomura, Y Okuda
    JOURNAL OF CRYSTAL GROWTH 237 47 - 50 0022-0248 2002/04 [Not refereed][Not invited]
     
    Melting of solid He-4 in a superfluid was observed when sound pulses were applied to the surface. Amount of melting was measured by changing the sound power and pulse numbers. It is not proportional to the power but to the square root of it. Both power and pulse number dependences are explained consistently if the melting coefficient is about 10% larger than that of the growth coefficient. (C) 2002 Elsevier Science B.V. All rights reserved.
  • R Nomura, M Maekawa, Y Suzuki, Y Okumura, Y Okuda
    JOURNAL OF LOW TEMPERATURE PHYSICS 126 (1-2) 39 - 44 0022-2291 2002/01 [Not refereed][Not invited]
     
    We observed the melting of solid He-4 in superfluid when the sound waves mere injected to its rough surface at 1.2 K. Single crystal was grown between two transducers and ultrasound pulses were applied normally to the solid-liquid inter face from solid side or liquid side. Amount, of melting was on the same order in both cases. We developed surface height measurement system using the sound wave itself and measured the amount of melting by changing the sound power and the number of pulses.
  • G Gervais, TM Haard, R Nomura, N Mulders, WP Halperin
    PHYSICAL REVIEW LETTERS 87 (3) 035701  0031-9007 2001/07 [Not refereed][Not invited]
     
    The effect of impurity scattering on the phase diagram of pure superfluid He-3 has been investigated by acoustic techniques near the bulk polycritical pressure. Impurities were introduced with a 98% porous silica aerogel. In zero applied field, the equilibrium phase is a B phase, consistent with predictions from isotropic scattering. The superfluid transition in a magnetic field at 25 bars is from normal to A phase and is independent of the magnetic field up to 2.9 kG. A first-order phase transition between A and B superfluids is observed with surprisingly strong supercooling in both zero and nonzero applied field.
  • G Gervais, TM Haard, R Nomura, N Mulders, WP Halperin
    PHYSICAL REVIEW LETTERS 87 (3) 0031-9007 2001/07 [Refereed][Not invited]
     
    The effect of impurity scattering on the phase diagram of pure superfluid He-3 has been investigated by acoustic techniques near the bulk polycritical pressure. Impurities were introduced with a 98% porous silica aerogel. In zero applied field, the equilibrium phase is a B phase, consistent with predictions from isotropic scattering. The superfluid transition in a magnetic field at 25 bars is from normal to A phase and is independent of the magnetic field up to 2.9 kG. A first-order phase transition between A and B superfluids is observed with surprisingly strong supercooling in both zero and nonzero applied field.
  • G Gervais, R Nomura, TM Haard, Y Lee, N Mulders, WP Halperin
    JOURNAL OF LOW TEMPERATURE PHYSICS 122 (1-2) 1 - 10 0022-2291 2001/01 [Not refereed][Not invited]
     
    An acoustic cavity containing He-3 in 98% porous silica aerogel was used to investigate the effects of impurity scattering in a Fermi liquid. The pressure and temperature dependence of the sound attenuation in the normal Fermi liquid was extracted from the cavity response. The attenuation of sound displays behavior very different from the bulk owing to strong elastic scattering of quasi-particles by the silica strands. Using a visco-elastic model of the Fermi liquid, we find a mean free path restricted to similar to 340 nm. Information on the sound velocity is inferred from the pressure dependence of the oscillation period of the cavity response. The data can be accounted for by a Biot model of the He-3 liquid in the porous aerogel.
  • R Nomura, G Gervais, TM Haard, Y Lee, N Mulders, WP Halperin
    PHYSICAL REVIEW LETTERS 85 (20) 4325 - 4328 0031-9007 2000/11 [Not refereed][Not invited]
     
    High-frequency (similar to 15 MHz) acoustics were performed on He-3 in 98% porous silica aerogel using an acoustic cavity technique. Measurements of the sound attenuation in the normal Fermi liquid and superfluid display behavior quite different from the bulk owing to strong elastic scattering of quasiparticles. The transition from first-to-zero sound is completely obscured with a quasiparticle mean-free path estimated to be in the range of 200-300 nm. No collective mode attenuation peak was observed at or below the superfluid transition.
  • R Nomura, M Yamaguchi, K Takaoka, Xu, X, Y Sasaki, T Mizusaki
    PHYSICAL REVIEW LETTERS 85 (14) 2977 - 2980 0031-9007 2000/10 [Not refereed][Not invited]
     
    We have measured the temperature dependence of the 10.98 MHz longitudinal sound velocity of solid He-3 in the nuclear-ordered U2D2 phase and in the paramagnetic phase along the melting curve. The temperature dependence of the sound was attributed to the contributions from the nuclear spin system and the molar volume change along the melting curve. The sound velocity increased with temperature as T-4 in the U2D2 phase and the sound anisotropy due to the exchange interaction was found to be about 10% among single-domain crystals investigated. The average value of the Gruneisen constant of the spin wave velocity in the ordered phase was <(gamma)over bar>(c) = 16 and is compared to the calculated value of the multiple-exchange model.
  • TM Haard, G Gervais, R Nomura, WP Halperin
    PHYSICA B 284 289 - 290 0921-4526 2000/07 [Not refereed][Not invited]
     
    The diffusion limited cluster aggregation (DLCA) model is a simple algorithm that simulates the growth of silica aerogels and can be used to compare with scattering experiments. In order to study the properties of helium liquids within aerogel we have extended application of the DLCA model to lengthscales larger than the mean free path. Of particular importance are the effects of the model's periodic boundary conditions. When these are accounted for the distribution function beyond a few hundred Angstroms develops into a simple exponential decay which can be extrapolated, allowing a precise determination of the mean free path, l. We find l is inversely proportional to the density, rho, over the range investigated, 0.001 < rho < 0.05. (C) 2000 Elsevier Science B.V. All rights reserved.
  • R Nomura, M Suzuki, M Yamaguchi, Y Sasaki, T Mizusaki
    PHYSICA B 280 (1-4) 140 - 141 0921-4526 2000/05 [Refereed][Not invited]
     
    The sound velocity of a single-domain He-3 crystal was measured in the nuclear-ordered low-held phase and the paramagnetic phase along the melting curve, using 10.98 MHz longitudinal sound. The temperature dependence of the sound velocity along the melting curve was explained by a nuclear spin contribution and the molar volume change along the melting curve. By comparing the measured velocity with thermodynamic quantities, we extracted the Gruneizen constant for the exchange energy. The anisotropy of the velocity in the ordered phase was investigated for three samples and was found to be smaller than 2 x 10(-5) in Delta nu/nu. The attenuation coefficient of the sound was much smaller than 0.2 cm(-1). (C) 2000 Elsevier Science B.V. All rights reserved.
  • R Nomura, A Uchida, M Suzuki, M Yamaguchi, Y Sasaki, T Mizusaki
    JOURNAL OF LOW TEMPERATURE PHYSICS 113 (5-6) 763 - 768 0022-2291 1998/12 [Not refereed][Not invited]
     
    Sound velocity of solid He-3 with an almost single magnetic domain was measured in the nuclear-ordered U2D2 phase and the paramagnetic phase along the melting curve using 10.98MHz longitudinal ultra-sound The sound velocity increased with temperatures as T-4 in the U2D2 phase and jumped about 0.1% at the nuclear-ordered temperature T-N. Above T-N, it increased gradually, going through a maximum around 4mK, and then decreased as temperature increased. The temperature dependence of the sound velocity a's attributed to two parts, the change an density of the solid along the melting curve and the temperature dependent internal energy of the nuclear spin. The nuclear spin contribution to the temperature dependent sound velocity agreed qualitatively with measured thermodynamical Quantities. Attenuation of the sound at 10.98MHz was smaller than 0.2(cm(-1)).
  • T Matsushita, R Nomura, HH Hensley, H Shiga, T Mizusaki
    JOURNAL OF LOW TEMPERATURE PHYSICS 105 (1-2) 67 - 92 0022-2291 1996/10 [Not refereed][Not invited]
     
    Pulsed NMR experiments have been performed on U2D2 solid He-3 with a single domain in high fields where the Larmor frequency was much larger than the zero-field antiferromagnetic resonance frequency. The free induction signal decayed rapidly under certain conditions. The rapid decay is attributed to the onset of the instability of the uniform precession. We propose a model for the instability due to the self-induced emission from the upper-mode magnon to the lower-mode magnon which is similar to the Suhl instability in electronic ferromagnets. A large negative frequency shift was observed during the rapid decay, which is consistently explained by the model. Under stable conditions of the spin motion outside of the instability region, we observed the tipping-angle-dependent frequency shift and multiple spin echoes, both of which agree well with Namaizawa's theory.
  • T Matsushita, R Nomura, HH Hensley, H Shiga, T Mizusaki
    JOURNAL OF LOW TEMPERATURE PHYSICS 105 (1-2) 67 - 92 0022-2291 1996/10 [Refereed][Not invited]
     
    Pulsed NMR experiments have been performed on U2D2 solid He-3 with a single domain in high fields where the Larmor frequency was much larger than the zero-field antiferromagnetic resonance frequency. The free induction signal decayed rapidly under certain conditions. The rapid decay is attributed to the onset of the instability of the uniform precession. We propose a model for the instability due to the self-induced emission from the upper-mode magnon to the lower-mode magnon which is similar to the Suhl instability in electronic ferromagnets. A large negative frequency shift was observed during the rapid decay, which is consistently explained by the model. Under stable conditions of the spin motion outside of the instability region, we observed the tipping-angle-dependent frequency shift and multiple spin echoes, both of which agree well with Namaizawa's theory.
  • T Matsushita, R Nomura, HH Hensley, H Shiga, T Mizusaki
    FIZIKA NIZKIKH TEMPERATUR 22 (2) 182 - 188 0132-6414 1996/02 [Not refereed][Not invited]
     
    Pulsed NMR experiments have been performed on U2D2 solid He-3 with a single domain in high fields. The free induction signal decayed rapidly under certain conditions. The rapid decay was attributed to the onset of an instability of uniform precession. We propose a model for the instability due to the self-induced emission from the upper-mode to lower-mode magnon branch, which is similar to the Suhl instability in electronic ferromagnets. Under stable conditions of the spin notion, we observed the tipping angle-dependent frequency shift and multiple spin echoes, which agrees well with Namaizawa's theory.
  • T Matsushita, R Nomura, HH Hensley, H Shiga, T Mizusaki
    FIZIKA NIZKIKH TEMPERATUR 22 (2) 182 - 188 0132-6414 1996/02 [Refereed][Not invited]
     
    Pulsed NMR experiments have been performed on U2D2 solid He-3 with a single domain in high fields. The free induction signal decayed rapidly under certain conditions. The rapid decay was attributed to the onset of an instability of uniform precession. We propose a model for the instability due to the self-induced emission from the upper-mode to lower-mode magnon branch, which is similar to the Suhl instability in electronic ferromagnets. Under stable conditions of the spin notion, we observed the tipping angle-dependent frequency shift and multiple spin echoes, which agrees well with Namaizawa's theory.
  • T Matsushita, R Nomura, HH Hensley, H Shiga, T Mizusaki
    CZECHOSLOVAK JOURNAL OF PHYSICS 46 (S6) 2995 - 3002 0011-4626 1996 [Not refereed][Not invited]
     
    Pulsed NMR was used to investigate nuclear spin dynamics of nuclear-ordered solid He-3 in the low field phase. The nuclear spill motion became unstable under certain conditions. Under stable conditions the spin motion can be described by the OCF equations. The tipping-angle-dependent frequency shift and multiple spin echoes were observed, which are similar to the case of superfluid He-3. The onset of the instability of spin motion is attributed to the stimulated emission mechanism through the three-magnon relaxation process, which is similar to the Suhl instability in electronic magnetism. We derived the magnon life time from the analysis of the instability. During the instability, a large negative frequency shift was observed. This negative shift is explained by the extension of Fomin-Ohmi's theory to include the state of decayed magnon and this explanation is consistent with the instability model.
  • R NOMURA, HH HENSLEY, T MATSUSHITA, T MIZUSAKI
    JOURNAL OF LOW TEMPERATURE PHYSICS 94 (5-6) 377 - 383 0022-2291 1994/03 [Refereed][Not invited]
     
    We have measured the growth rate of single crystal U2D2 solid He-3 in the superfluid B phase as a function of chemical potential difference DELTAmu between the solid and liquid for temperatures between 0.4 and 0.9 T(N). The growth rate was not proportional to DELTAmu, with very slow growth rates for DELTAmu less than about 10 erg/cm3. For larger values of DELTAmu the growth rate depended weakly on temperature and the growth was attributed to a quantum growth mechanism due to screw dislocations. The melting rate was too fast to be measured quantitatively, but was slower at higher temperatures
  • T MATSUSHITA, R NOMURA, HH HENSLEY, K FUKUDA, T MIZUSAKI, A HIRAI
    PHYSICA B 194 929 - 930 0921-4526 1994/02 [Refereed][Not invited]
     
    Pulsed NMR experiments have been performed on monodomain U2D2 solid He-3 in high magnetic fields. It was found that the frequency of the free induction signal changed with time, and in some cases a negative frequency shift as large as 20 kHz from the Larmor frequency was observed. The precession frequency immediately following the rf pulse agreed with Namaizawa's theory, however the free induction signal decayed rapidly. We attribute this to the instability of the uniform precession due to the creation of spin waves, but find disagreement with the instability criterion predicted by Ohmi et al. and Shopova.
  • Nonlinear Spin Dynamics in the U2D2 Phase of Nuclear-ordered Solid 3He
    T. Matsushita, R. Nomura, H.H. Hensley, K. Fukuda, T. Mizusaki A. Hirai
    Physica B 194 901 - 902 1994 [Not refereed][Not invited]
  • T MATSUSHITA, R NOMURA, K FUKUDA, T MIZUSAKI, A HIRAI
    JOURNAL OF LOW TEMPERATURE PHYSICS 89 (1-2) 365 - 373 0022-2291 1992/10 [Refereed][Not invited]
     
    Pulsed NMR experiments have been performed on U2D2 solid He-3 with a single domain at high magnetic fields. It was found that the frequency of the free induction signal changed with time. In some cases, a large negative frequency shift of about 2 kHz from the Larmor frequency was observed some time after the rf pulse, after which frequency returned to that observed for a small tipping angle. The tipping-angle-dependent frequency shift, which was taken to be the precession frequency immediately following the rf pulse, agreed with Namaizawa's theory. The free induction signal showed a decay behavior similar to that of superfluid He-3-A. This can be attributed to the instability of the uniform precession due to the creation of spin wave modes, but does not agree with the instability criterion predicted by Ohmi et al. and Shopova.

MISC

  • Anomalous Oscillation Modes of Superfluid 4He Droplets
    S. Takamatsu, K. Miyake, R. Yamane, R. Nagatomo, K. Onodera, Y. Aoki, R. Nomura  New Frontiers in Advanced Magnetism 2024  2024/08
  • Robust Discretization of Dripping Periods of Superfluid 4He
    R. Yamane, K. Miyake, S. Takamatsu, R. Nagatomo, K. Onodera, Y. Aoki, R. Nomura  New Frontiers in Advanced Magnetism 2024  2024/08
  • Novel Oscillation Modes of Pendant Droplets of Superfluid 4He
    K. Miyake, R. Yamane, S. Takamatsu, K. Onodera, R. Nagatomo, Y. Aoki, R. Nomura  The 2024 International Symposium on Quantum Fluids and Solids (QFS2024)  2024/07
  • Anomalous Dripping of Superfluid Droplets
    K. Onodera, R. Nagatomo, K. Miyake, S. Kashimo, Y. Aoki, R. Nomura  International Conference on Quantum Liquid Crystals 2023 (QLC2023)  2023/08
  • Quantized Dripping Period of Superfluid 4He
    R. Nagatomo, K. Onodera, K. Miyake, S. Kashimoto, Y. Aoki, R. Nomura  International Conference on Quantum Liquid Crystals 2023 (QLC2023)  2023/08
  • Robust quantization of dripping period for superfluid 4He droplets
    R. Nomura, R. Nagatomo, K. Onodera, K. Miyake, S. Kashimoto, Y. Aoki  28th International Conference on Statistical Physics, Statphys28  2023/08
  • Dripping character of superfluid 4He droplets
    K. Onodera, R. Nagatomo, S. Kashimoto, Y. Aoki, R. Nomura  International Conference on Ultra Low Temperature Physics (ULT2022)  2022/08  [Not refereed][Not invited]
  • Increasing the film flow rate of 4He by coating
    K. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura  International Conference on Ultra Low Temperature Physics (ULT2022)  2022/08  [Not refereed]
  • Dripping Period of Superfluid 4He due to Film Flow
    R. Nagatomo, K. Onodera, S. Kashimoto, Y. Aoki, R. Nomura  International Conference on Ultra Low Temperature Physics (ULT2022)  2022/08  [Not refereed][Not invited]
  • Dripping Period of Superfluid 4He via Film Flow
    R. Nagatomo, K. Onodera, S. Kashimoto, R. Nomura  29th International Conference on Low Temperature Physics  2022/08  [Not refereed][Not invited]
  • Enhancing the Film Flow of Superfluid 4He by Coating
    K. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura  29th International Conference on Low Temperature Physics  2022/08  [Not refereed][Not invited]
  • Falling Behavior of Superfluid 4He Droplets
    K. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura  29th International Conference on Low Temperature Physics  2022/08  [Not refereed][Not invited]
  • Ueno K., Osawa A., Mimori T., Kato H., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  63-  (2)  709  -709  2008/08/25
  • Tamura Y., Murakawa S., Wada Y., Wasai M., Saitoh M., Aoki Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  63-  (2)  719  -719  2008/08/25
  • Wada Y., Nishida R., Saitoh M., Aoki Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  60-  (2)  669  -669  2005/08/19
  • Abe H., Saitoh Y., Ueda T., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  60-  (2)  666  -666  2005/08/19
  • Abe H., Ogasawara F., Saitoh Y., Ueda T., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  60-  (1)  764  -764  2005/03/04
  • Saitoh M., Aoki Y., Wada Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  60-  (1)  763  -763  2005/03/04
  • Miyashita W., Yoneyama K., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  59-  (2)  714  -714  2004/08/25
  • Wada Y., Aoki Y., Ogino A., Taniguchi J., Saitoh M., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  59-  (2)  708  -708  2004/08/25
  • Ogasawara F., Kimura S., Tatara T., Abe H., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  59-  (1)  822  -822  2004/03/03
  • Aoki Y., Wada Y., Ogino A., Saitoh M., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  59-  (1)  815  -815  2004/03/03
  • Ogasawara F., Kimura S., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  58-  (2)  693  -693  2003/08/15
  • Aoki Y., Sekimoto Y., Wada Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  58-  (1)  759  -759  2003/03/06
  • Aoki Y., Yamaguchi W., Sekimoto Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  56-  (2)  640  -640  2001/09/03
  • Maekawa M., Suzuki Y., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  56-  (1)  728  -728  2001/03/09
  • Aoki Y., Yamaguchi W., Nomura R., Matsumoto K., Okuda Y.  Meeting abstracts of the Physical Society of Japan  56-  (1)  720  -720  2001/03/09
  • Okumura Y., Maekawa M., Nomura R., Okuda Y.  Meeting abstracts of the Physical Society of Japan  55-  (2)  670  -670  2000/09/10
  • Nomura R., Uchida A., Suzuki M., Hensley H.H., Sasaki Y., Mizusaki T.  Meeting abstracts of the Physical Society of Japan  52-  (2)  615  -615  1997/09/16
  • Matsushita T, Nomura R, Hensley H.H., Shiga H, Fukuda K, Mizusaki T  Abstracts of the meeting of the Physical Society of Japan. Annual meeting  50-  (3)  434  -434  1995/03/16
  • Models for the Growth Mechanisms of Frost Heave in Helium
    R. Nomura, T. Mizusaki  111  -120  1995  [Not refereed][Not invited]
  • Matsushita T., Nomura R., Hensley H.H., Fukuda K., Mizusaki T., Hirai A.  Abstracts of the meeting of the Physical Society of Japan. Annual meeting  48-  (3)  274  -274  1993/03/16
  • Matsushita T., Nomura R., Fukuda K., Mizusaki T., Hirai A.  年会講演予稿集  46-  (3)  233  -233  1991/09/12

Books etc

  • Equilibrium and Non-equilibrium Shapes of 4He Quantum Crystals in Superfluid
    野村竜司, 奥田雄一 
    日本結晶成長学会誌 47巻4号 03-1-10（2020） 2020
  • 多孔体中における量子結晶成長と自己組織化臨界性
    野村竜司 
    ホソカワ粉体工学振興財団年報、No. 23, 142-147 (2015) 2015
  • 第２７回 低温物理国際会議（LT27)報告
    村上修一, 野村竜司, 宮川和也 
    固体物理 50, 3, 49-56 (2015) 2015
  • エアロジェル中における4He量子結晶の雪崩的成長と冪乗則
    野村竜司, 奥田雄一 
    固体物理 47, 9, 37-47 (2012) 2012
  • トポロジカル超流動3He-B相の表面マヨラナコーン
    野村竜司 
    新学術領域研究｢対象性の破れた凝縮系におけるトポロジカル量子現象｣ニュースレター、 No. 2, 22-26 (2012) 2012
  • 量子固体の結晶成長(2009年物性若手夏の学校サブゼミ講義ノート)
    野村竜司 
    物性研究vol. 93, 935-955 (2010) 2010
  • The new aspect of 4He crystal growth and a possible experiment on the jet plane
    Y. Okuda, R. Nomura 
    J. Jpn. Soc. Microgravity Appl. 24, 2, 183-187 (2007) 2007
  • 音響放射圧で駆動する固体ヘリウム4の結晶成長
    阿部陽香, 野村竜司, 奥田雄一 
    固体物理 41, 10, 669-677 (2006) 2006
  • ヘリウム負結晶の運動
    野村竜司, 奥田雄一 
    パリティー, 21, 08, 52-55 (2006) 2006
  • 核整列固体３Heにおける超音波測定
    野村 竜司 
    京都大学極低温研究室月報 73, 1-9 (1998) 1998

Presentations

  • 平衡から大きく離れた4He量子結晶と超流動4He液滴
    野村竜司
    京都大学物理学第一教室大学院特別講義１談話会  2024/09
  • Quantum Dripping of Superfluid 4He  [Invited]
    R. Nomura
    The 2024 International Symposium on Quantum Fluids and Solids (QFS2024)  2024/07
  • 超流動液体から生成する4He量子結晶の非平衡形
    野村竜司
    北海道大学第3回応用物理学コロキウム  2022/12
  • Quantum Crystallizations of 4He Far from Equilibrium  [Invited]
    R. Nomura
    29th International Conference on Low Temperature Physics  2022/08
  • Higgs Modes and Surface Majorana Modes in Topological Superfluid 3He  [Invited]
    野村竜司
    第2回初期宇宙相転移ダイナミクスに迫る物性実験勉強会（オンライン開催）  2022/05
  • トポロジカル超流動3He-B相の表面マヨラナ状態の観測  [Invited]
    ヘリウム・オンラインセミナー 第２７回  2021/12
  • 超流動液体中で大変形した4He結晶の動態  [Invited]
    野村竜司
    電気通信大学 2021年度物理工学セミナー  2021/09
  • Falling of 4He Crystals in Superfluid  [Invited]
    R. Nomura, Y. Okuda
    QFS2021 International Online Conference  2021/08
  • 平衡から大きく離れた固体4Heの結晶形  [Invited]
    野村竜司
    東京工業大学 量子物理学・ナノサイエンスセミナー  2021/05
  • 超流動流の影響を受けた4He結晶の非平衡形  [Invited]
    野村竜司
    ヘリウム・オンラインセミナー  2020/12
  • 平衡下および非平衡下における4Heの結晶形  [Invited]
    野村竜司
    ワークショップ「固液を区別するパラメタ―長距離秩序か配向秩序か―」  2019/12
  • 超流動3He-B相の表面マヨラナ励起  [Invited]
    野村竜司
    新学術領域研究「トポロジーが紡ぐ物質科学のフロンティア」 第12回トポロジー連携研究会「マヨラナ励起の実証に向けて」  2019/11
  • Liquid Pocket Formation and Its Crystallization Onset via Mass Flow through Solid 4He in Aerogel  [Invited]
    R. Nomura, Y. Okuda
    International Conference on Quantum Fluids and Solids (QFS2019)  2019/08
  • 機械振動子を用いたトポロジカル超流体研究の進展  [Invited]
    野村竜司
    日本物理学会 シンポジウム｢超低温技術が切り拓く超流動・超伝導研究の新展開｣  2019/03
  • Crystallization Dynamics of 4He in Aerogels  [Invited]
    R. Nomura
    12th International Conference on Cryocrystals and Quantum Crystals  2018/08
  • Inchworm Driving of 4He Crystals in Superfluid  [Invited]
    R. Nomura, T. Yoshida, A. Tachiki, Y. Okuda
    International Symposium on Quantum Fluids and Solids 2018  2018/07
  • トポロジカル超流動3Heの新奇準粒子状態  [Invited]
    野村竜司
    日本物理学会 シンポジウム「超伝導物質および超流動ヘリウム研究の切り開くトポロジカル物理の最前線」  2017/09
  • Crystallization dynamics of 4He far from equilibrium  [Invited]
    Ryuji Nomura
    ULT 2017 Frontiers of Low Temperature Physics  2017/08
  • Anomalous Asymmetry in Melting and Growth Relaxations of 4He Crystals after Manipulation by Acoustic Radiation Pressure  [Not invited]
    R. Nomura, H. Abe, Y. Okuda
    The 28th International Conference on Low Temperature Physics  2017/08
  • 4He Crystals in Superfluid out of Equilibrium  [Invited]
    R. Nomura
    University of Florida, Department of Physics, Colloquium  2017/03
  • Avalanche Crystallization of 4He in Aerogel  [Not invited]
    R. Nomura, Y. Okuda
    Avalanches, plasticity, and nonlinear response in nonequilibrium solids  2016/03
  • トポロジカル超流動3Heのヒッグスモードと表面マヨラナモード  [Invited]
    野村竜司
    金沢大学理学談話会  2015/12
  • 超流動3Heにおけるトポロジカル量子相転移の探索  [Invited]
    野村竜司, 秋山綱紀, 奥田雄一
    文部科学省科学研究費補助金 新学術領域研究「トポロジーが紡ぐ物質科学のフロンティア」第１回領域研究会  2015/12
  • 超音波で探る超流動3Heのヒッグスモードと表面マヨラナ状態  [Invited]
    野村竜司
    日本物理学会 シンポジウム「多自由度性が織りなす異方的超流体の新しい物理」  2015/09
  • Experimental Search for Majorana Fermion in 3He-B; Achievements and Challenges  [Invited]
    R. Nomura
    Grand Challenges in Quantum Fluids and Solids Workshop  2015/08
  • Magnetic Field Effects on the Surface Majorana Bound States of Superfluid 3He B-phase  [Invited]
    R. Nomura, M. Wasai, K. Akiyama, M. Mashino, T. Nakao, S. Murakawa, Y. Okuda
    International Conference on Topological Quantum Phenomena
  • Magnetic field effects on surface Majorana fermions of superfluid 3He-B  [Not invited]
    R. Nomura, M. Wasai, K. Akiyama, M. Mashino, T. Nakao, S. Murakawa, Y. Okuda
    27th International Conference on Low Temperature Physics (LT27)  2014/08
  • 4Heの結晶成長；その普遍性と特異性  [Invited]
    野村竜司
    東工大物性セミナー  2014/06
  • 乱れの下で進行する量子固体の結晶化  [Invited]
    京都大学物理学第一教室佐々研究室セミナー  2013/09
  • Self-organized criticality in quantum crystallization of 4He in aerogel  [Invited]
    R. Nomura, H. Matsuda, A. Ochi, R. Isozaki, Y. Okuda
    International Conference on Quantum Fluids and Solids (QFS2013)  2013/08
  • Power Law Behavior in Quantum Crystallization of 4He in Aerogel  [Not invited]
    R. Nomura, H. Matsuda, A. Ochi, R. Isozaki, Y. Okuda
    STATPHYS25, the 25th International Conference on Statistical Physics  2013/07
  • Surface Majorana cone of the topological superfluid 3He B phase  [Invited]
    R. Nomura
    APS March Meeting 2013, Invited Session: Superfluids under Nanoscale Confinement  2013/03
  • Surface Majorana Cone of the Topological Superfluid 3He B Phase  [Invited]
    R. Nomura
    International Conference on Topological Quantum Phenomena  2012/05
  • Andreev-Majorana bound states on the superfluid 3He-B surface  [Invited]
    R. Nomura
    Microkelvin workshop 2012  2012/03
  • Surface Majorana Cone of the Superfluid 3He B Phase  [Invited]
    R. Nomura
    International Workshop for Young Researchers on Topological Quantum Phenomena  2011/11
  • Surface Majorana Cone of the Superfluid 3He B Phase  [Invited]
    R. Nomura
    ULT2011, the new frontiers of low temperature physics  2011/08
  • 超音波で探る量子界面：超流動３Heの表面束縛状態と固体４Heの結晶成長  [Invited]
    野村竜司
    東京大学物性研究所セミナー  2011/07
  • 不規則媒質中での量子固体の結晶化に見られる動的転移と臨界性  [Invited]
    野村竜司
    青山学院大学 物理・数理学科コロキウム  2011/06
  • 超音波で探る固体４Heの結晶成長・超流動３Heの表面状態  [Invited]
    野村竜司
    大阪市立大学第３回『アインシュタインの物理』でリンクする研究・教育拠点研究会  2010/10
  • Surface Andreev Bound States and Surface Majorana Fermions on the Superfluid 3He B Phase  [Invited]
    R. Nomura
    University of Florida, Department of Physics, Seminar  2010/03
  • Thermal and quantum crystallizations of 4He in aerogel  [Not invited]
    R. Nomura, R. Masumoto, K. Ueno, Y. Okuda
    APS March Meeting  2010/03
  • Surface Andreev Bound States and Surface Majorana States on the Superfluid 3He B Phase  [Not invited]
    R. Nomura, S. Murakawa, Y. Wada, M. Wasai, K. Akiyama, Y. Tamura, M. Saitoh, Y. Aoki, Y. Okuda
    International Symposium on Physics of New Quantum Phases in Superclean Materials  2010/03
  • Surface Andreev Bound States in Superfluid 3He-B  [Invited]
    R. Nomura, S. Murakawa, Y. Wada, M. Wasai, K. Akiyama, Y. Tamura, M. Saitoh, Y. Aoki, Y. Okuda
    International Symposium on Novel Spin Pairing 2009 (NSP2009)  2009/09
  • 量子固体の結晶成長  [Invited]
    野村竜司
    物性物理夏の学校 サブゼミ
  • ヘリウムの結晶成長；その普遍性と特異性  [Invited]
    野村竜司
    スーパークリーン特定・若手夏の学校  2008/08
  • Surface Andreev bound states of superfluid 3He on a specularity-controlled wall  [Not invited]
    R. Nomura, S. Murakawa, Y. Wada, Y. Tamura, M. Saitoh, Y. Aoki, Y. Okuda, Y. Nagato, M. Yamamoto, S. Higashitani, K. Nagai
    25th international conference on Low Temperature Physics (LT25)  2008/08
  • 超流動体から生じるヘリウム結晶の特異な成長過程  [Invited]
    野村竜司
    東工大宇宙物理学理論研究室セミナー  2008/06
  • 平衡から大きく外れた４Ｈｅ結晶  [Invited]
    野村竜司
    日本物理学会第６２回年会 若手奨励賞招待講演  2007/09
  • Avalanche growth of 4He crystals in aerogels  [Not invited]
    R. Nomura, A. Osawa, T. Mimori, H. Kato, Y. Okuda
    The International Conference on Science of Friction  2007/09
  • Dynamical Phase Transition of 4He Crystals in Aerogels  [Not invited]
    Ryuji Nomura, Haruko Kato, Aiko Osawa, Yuichi Okuda
    Physics of superclean materials International Workshop “Physics of Supersolids and Related Topics”  2007/04
  • 音響放射圧によるヘリウムの結晶成長  [Invited]
    野村竜司
    東大駒場物性セミナー  2006/12
  • Transverse Acoustic Impedance of Superfluid 3He and Surface Andreev Bound States  [Invited]
    R. Nomura, Y. Wada, R. Nishida, M. Saitoh, Y. Aoki, S. Murakawa, Y. Okuda
    International symposium on quantum fluids and solids  2006/08
  • Anisotropic Interface Motion of 4He Crystal in an Acoustic Field  [Not invited]
    R. Nomura, F. Ogasawara, Y. Saitoh, H. Abe, Y. Okuda
    Todai International Symposium 2004 and The Ninth ISSP International Symposium on Quantum Condensed System  2004/11
  • High-Speed Dynamics in Largely Deformed Crystal-Superfluid Interface of 4He  [Not invited]
    R. Nomura, F. Ogasawara, Y. Saitoh, H. Abe, Y. Okuda
    Vortex and Turbulence in Classical and Quantum Fluids  2004/10
  • Nucleation and Growth of 4He Crystal by Acoustic Radiation Pressure  [Invited]
    R. Nomura
    Workshop on Ultra-low Temperature Physics (ULT)  2002/08
  • エアロジェル中３Heの超音波測定  [Invited]
    野村竜司
    日本物理学会第５６回年会  2001/03
  • 超流動３Heにおける不純物効果 Dirty Superfluid  [Invited]
    野村竜司
    東工大物性セミナー  2000/06

Association Memberships

  • 日本物理学会   ナノ学会   

Research Projects

  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    Date (from‐to) : 2022/04 -2025/03 
    Author : 野村 竜司
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    Date (from‐to) : 2017/04 -2021/03 
    Author : 野村 竜司, 阿部 陽香
     
    微小機械振動子（micro electromechanical systems, MEMS）などの新しいタイプの力学センサーを用いた局所観測により、ナノメートルスケールの狭い空間中に閉じ込めた超流動ヘリウム3を調べ、ナノ超流動ヘリウム3の相図を明らかにすることを目的とする。ナノ空間中では、様々な閉じ込めの形状に応じて、2次元A相、ストライプ相、ヘリカル相、ポーラー相などの新相が理論的に提案されている。ヒッグスモードによる高周波音波の共鳴吸収やMEMSの力学応答測定から各相の対称性が決定を目指している。 高磁場中で実現する非ユニタリー超流動ヘリウム3であるA1相、A2相において、水晶振動子の高周波横波インピーダンス測定から、表面束縛状態がスピン状態に依存する応答を示すことが、過去の代表らによる研究で明らかにされた。これを海外共同研究者との共同研究により、さらに推し進める。スピン状態依存する力学応答の起源を、水晶振動子とMEMSの同時測定による幅広い周波数域での力学応答から明らかにすることが、共同研究の目的である。また磁場中で、振動子をその場回転させて、力学応答の磁場との角度依存性を測定することも、本共同研究の大きな特徴である。高磁場中の超流動ヘリウム3の高周波横波インピーダンス測定のセットアップを終えて、全体を組み上げ冷却実験を開始した。しかし、横波インピーダンスとMEMSの同測定を行うと、MEMS測定に不具合が生じることは分かり、その対応に予想外に実験時間がかかっている。現在は、超低温実験を継続中である。 また、マヨラナ粒子に関する国内研究会、結晶秩序に関する国内ワークショップでの、招待講演を行った。量子流体、固体の国際会議において、ナノスケールの乱れの下でのヘリウム4の結晶化についての招待講演を行った。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    Date (from‐to) : 2016/04 -2018/03 
    Author : 野村 竜司
     
    磁場中の超流動3Heの音響抵抗測定のセットアップを終えて、全体を組み上げた。その後、冷却を試みたが大きな熱流入があり、超低温での実験はまだ出来ていなかった。熱流入の原因を探ったところ、新たに導入した超伝導マグネットのリード線からの熱流入が原因であることを突き止めたが、磁場中測定を行うまでは行かなかった。 ゼロ磁場での測定が可能な、バルク3Heと壁との間に生じる4He薄膜の超流動転移を調べた。4Heの固化圧よりも高圧側にも関わらず、壁での3He準粒子散乱に対する鏡面度が増大していることを見出した。これは4He薄膜が固化しているにも関わらず、壁の乱れを抑制することを示す結果である。 MEMS(micro electromechanical systems)を用いたナノ薄膜超流動3Heの力学応答を調べる研究は、海外共同研究者との共同研究により進展した。過去に我々が行った高磁場中で実現する超流動3HeのA1相、A2相における高周波横波抵抗測定により、これらの非ユニタリー超流動の表面状態は力学応答に大きなスピン状態依存性を持つことが示されていた。この依存性は、単純な弱結合理論では説明できず、表面状態における強相関効果を捉えていると考えられる。in situ回転が可能な試料容器を用いて、横波音響抵抗測定とMEMS測定を磁場中で同時に行い、非ユニタリー超流動の表面状態の特異な力学応答を調べる準備をした。周波数依存性と磁場方位依存性からスピン状態依存性の起源を解明するべく、試料セルを組み立て、実験準備を終えた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2014/04 -2018/03 
    Author : Nomura Ryuji
     
    It was demonstrated that a 4He crystal can undergo motion on an oscillating plate as the result of employing an inchworm driving, a technique that is employed to impart motion, based on the difference between static and dynamic friction forces. However, the observed motion was quite different from the ordinary behavior of classical objects. The movement of these quantum crystals can be attributed to the anomalously quick crystal-superfluid transition, namely crystallization on one side and melting on the other, assisted by superflow induced during the oscillation. It was demonstrated that controlling the contact angle of a 4He crystal in superfluid is possible on a rough wall. From the comparison of the contact angles and SEM image of the rough wall, the Cassie-Baxter state was likely to be realized on it; the 4He crystal had a direct contact with the protruding parts of the rough surface but superfluid was entrapped between the crystal and the hollow parts of the wall.
  • Investigating Spin Degrees of Freedom of Surface Andreev Bound States of Non-unitary Superfluid Helium Three in High Magnetic Fields
    National High Magnetic Field Laboratory：User Program
    Date (from‐to) : 2017
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2010/04 -2016/03 
    Author : MAENO Yoshiteru, TANAKA Yukio, ISHIKAWA Osamu, ZHENG Guo-qing, KASHIWAYA Satoshi, ASANO Yasuhiro, NOMURA Ryuji, ANDO Yoichi, SATO Masatoshi, UEDA Masahito
     
    平成27年度は研究成果とりまとめにあたり、主に次の二点を行った。
    第一に、領域活動によるこれまでの研究成果を事後評価報告書にまとめ上げ、文科省でのヒアリングを経て事後評価を受けた。結果は評価A+をいただいた。総合所見において、「本研究領域は世界をリードする多くの研究成果を生み出し、当該学問分野における我が国の国際的優位性の確保と、その向上に大きく貢献した。また、積極的にアウトリーチ活動が実施されたことは、物性物理学における新しい概念の普及という点で高く評価できる。本研究領域の活動によって、多くの若手研究者が育成されたと認められる。」との評価をいただいた。報告書作成に際しては、領域メンバーからの成果情報を収集・集積して、発表論文、招待講演、受賞などに含まれる研究成果内容の分析を加えたうえで、今後の展望も含めた。また、新学術プロジェクトならではの、異なる専門分野研究者間の連携による研究成果・論文成果、5回開催(そのうち2回は国際会議として開催)した領域研究会の成果、17回開催した「集中連携研究会」の成果、若手育成のための若手国際会議や若手相互滞在プログラムの成果、市民講座や出前講義の成果の分析も行った。
    第二に、本領域の研究活動から生み出されたトポロジカル量子現象に関する新学術領域をさらに発展させるための活動を行った。まず、引き続き領域のHP と事務局を維持し、研究成果情報の収集と公開に務めるとともに、トポロジカル量子現象の研究に関わる研究者に対しての情報ソース・フォーラムとしての機能も果たし続けた。幸い、後継新学術領域プロジェクト「トポロジーが紡ぐトポロジカル物質科学のフロンティア」が採択されたので、さらに飛躍的な発展を生むために必要な引き継ぎ活動を行った。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2010/04 -2015/03 
    Author : ISHIKAWA Osamu, NOMURA Ryuji, HIGASHITANI Seiji, MIYAKE Kazumasa, TAKAGI Takeo, NAKAHARA Mikio, IKEGAMI Hiroki, OBARA Ken, MATSUMOTO Koichi, TAKEUCHI Hiromitsu, KUBOTA Minoru
     
    Superfluid 3He has two types of superfluid state, one is the time reversal symmetry breaking A phase and another is the orbit-spin symmetry breaking B phase. We have investigated the topological quantum phenomena at the interface or the boundary and obtained notable results as below. We showed the first evidence of the macroscopic angular momentum in the A phase and that of the Majorana cone of the surface bound state in the B phase. The local chirality of the A phase is also observed. We theoretically concluded that the density of state at the surface exactly corresponds to the amplitude of odd frequency pairing state. We also established new method of considering the odd frequency bulk superconductor, which includes the Meissner effect, by using the retarded pairing potential.
  • 多孔体中における量子結晶成長と自己組織化臨界性
    ホソカワ粉体工学振興財団：平成25年度ホソカワ粉体工学振興財団研究助成
    Date (from‐to) : 2014/03
  • トポロジカル超流動ヘリウム3の表面マヨラナコーンの発見
    東京工業大学理学系：平成24年度東京工業大学理学系若手研究奨励賞
    Date (from‐to) : 2012/12
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2010 -2012 
    Author : OKUDA Yuuichi, NOMURA Ryuji
     
    Superfluid 3He is an intensively investigated and well characterized p-wave superfluid. In the bulk BW state, which is commonly called 3He B phase, the superfluid gap is opened isotropically but near a flat boundary such as a wall of a container it can harbor interesting quasi-particle states inside the gap. These states are called surface Andreev bound states, and have not been experimentally explored in detail. Transverse acoustic impedance measurement has revealed their existence and provided spectroscopic details of the dispersion of the bound states. Recent theoretical arguments claim that the surface Andreev bound states of superfluid 3He B phase can be recognized as the edge states of the topological superfluid and be regarded asa Majorana fermion, a fancy particle which has not been confirmed in elementary particle physics. In this review, we present up-to-date knowledge on the surface Andreev bound states of 3He B phase revealed by acoustic spectroscopy and the possible realization of a Majorana fermion, along with related studies on this topic.
  • International Workshop for Young Researchers on Topological Quantum Phenomena in Condensed Matter with Broken Symmetries
    Asia Pacific Center for Theoretical Physics：External Activity for the Asia Pacific Center for Theoretical Physics, 2011
    Date (from‐to) : 2011/11
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2009 -2011 
    Author : NOMURA Ryujl, OKUDA Yuichi
     
    ^4He crystals were blown off by acoustic radiation pressure and floated in the superfluid under the reduced gravity condition. Apiece of stainless steel buried in a^4He crystal was driven by the inch-warm method of piezo crystal. We succeeded in operating the piezo crystal at very low temperatures and are ready to apply it to He crystals. Crystallization of He was investigated in aerogels and self-organized criticality in quantum tunneling was discovered.
  • 日本学術振興会：科学研究費助成事業 特定領域研究
    Date (from‐to) : 2008 -2009 
    Author : 野村 竜司
     
    超流動ヘリウム3では、ギャップエネルギーΔ以下に有限の表面準粒子状態密度が存在するが、これがアンドレーエフ束縛状態である。壁の鏡面度Sを大きくするにしたがい、この束縛状態バンドのバンド幅Δ^*が広がり、ゼロエネルギーの表面状態密度が減少すると予測されていた。S=1の極限では、表面状態密度はエネルギーに比例して増加する。このエネルギーに対する線形の依存性は、表面準粒子の分散関係が運動量に線形に依存することと等価であり、S=1でマヨラナコーンが存在することを意味する。我々はSが大きくなると、低エネルギーで新たなピークが現れることを見出した。またバンド幅が増大し、大きなSの領域でギャップレスとなることを確かめた。理論との比較により、この低エネルギーピークは、ゼロエネルギーの表面状態密度が減少することによって現れることが明らかとなった。観測されたSの増加による低エネルギーピークの成長は、ゼロエネルギーの表面状態密度が減少し、マヨラナコーンへと漸近する振る舞いであることを示した。S=1の極限で現れると予測されているマヨラナコーンの存在を強く支持する実験結果である。これまでマヨラナフェルミオンを観測したという明確な結果が無い中で、超流動ヘリウム3の表面マヨラナフェルミオンの存在を示す結果は大きな意味を持つ結果と考えられる。また11Tまでの高磁場でのインピーダンス測定から、A1相とA2相の温度変化が大きく異なり、弱結合の理論的振る舞いからずれることを見出した。強結合効果を取り入れた理論の進展が望まれる。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2007 -2008 
    Author : NOMURA Ryuji, OKUDA Yuichi
     
    超流動ヘリウム3のB相における表面状態密度には、超流動ギャップエネルギー以下に束縛状態バンドが現れる。このバンド幅が、壁の鏡面度が大きくなるに従い広くなることを見出した。また音響インピーダンスの温度依存性に新たな異常が表れることを観測した。この異常は有限の鏡面度のとき、表面状態密度のゼロエネルギー状態が強く抑制されることによって説明された。
  • 量子固体の結晶成長のダイナミクスにみられる新現象の解明と微小重力実験
    日本宇宙フォーラム：平成17,18,19宇宙環境利用に関する地上実験研究
    Date (from‐to) : 2005 -2007
  • エアロジェル中でのヘリウム結晶化過程の可視化
    ホソカワ粉体工学振興財団：平成18年度ホソカワ粉体工学振興財団研究助成
    Date (from‐to) : 2007/01
  • 液体ヘリウム中での気泡運動の可視化
    東京工業大学極低温物性研究センター：短期プロジェクト研究
    Date (from‐to) : 2006
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2003 -2005 
    Author : NOMURA Ryuji, OKUDA Yuichi
     
    We observed the very fast growth of the c-facet of a S^4$He crystal induced by acoustic waves. The growth velocity cannot be explained by the spiral growth model for the known values of the step mobility. We developed a new crystal growth mechanism of the facet by high power acoustic waves. Considering the first order effect of the oscillating pressure of the acoustic wave, steps are accelerated to the order of the sound velocity. Collisions of such high speed steps can induce the multiplication of steps as Parshin and Tsymbalenko suggested and lead to the larger step density than that of the spiral growth. This model reproduces the observed power and temperature dependence well and also has a quantitative agreement with the experiment.
  • 超流動ヘリウム３における表面量子状態の超音波分光
    倉田記念日立科学技術財団：平成１６年度倉田記念日立科学技術財団倉田奨励金
    Date (from‐to) : 2005
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2003 -2004 
    Author : 野村 竜司, 奥田 雄一
     
    我々は超音波を用いるとヘリウム4結晶を自由に成長、融解、核生成できることを発見した。これは音響放射圧によるものと考えている。超音波パルスによって生成する準安定状態の超流動ヘリウム4中の結晶核生成を系統的に調べた。2msecの超音波の存在下で到達できた準安定液体の臨界過加圧量の温度依存性は、低温おいては超音波強度が増すにつれて過加圧量が減少するが、高温では超音波の影響が見られなくなった。この温度依存性は我々がこれまでに調べたバルクの結晶表面への音響放射圧の効果と矛盾しないものである。また熱の影響を調べるために熱パルスによる核生成実験もあわせて行った。 また音響放射圧を利用して、結晶中に制御して負結晶を生成できることを見出した。その負結晶の移動様式と形態を系統的に調べた。ラフニング転移より高温のbcc固体では負結晶の形は球形であった。その運動は重力で真上に上昇していくものであり、その形態にも運動にも全く異方性は無かった。hcp固体ではラフニング転移に以下において形態が一変し、上面にはc-ファセットが現われ下面は滑らかな曲面になった。負結晶の移動に伴って上面が融解し下面が結晶化するわけであるが、上面では移動速度の遅いファセット面が広がり下面では移動速度の速いラフ面が広がったと考えれば説明がつく。言わば結晶の成長形と融解系を半分ずつくっ付けたようなものであり、負結晶の運動様式と深く結びついた形態である。また負結晶は真上には上昇せず、このファセットに平行な斜め上方に移動して行った。ファセット面は非常に易動度が小さいので、負結晶の形態と運動は異方的なものとなった。また0.9K以下で上昇速度が減少した。これはa-ファセットが側面に出現したためであると考えている。温度を下げるにしたがって負結晶の形態と運動が逐次的に異方性を増していく様子が観測できた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2002 -2004 
    Author : OKUDA Yuichi, NOMURA Ryuji
     
    3He sets into the P-wave spin-triplet super fluid phase at around 1 mK. Order parameter of the super fluid has a lot of internal degrees of freedom and hence it can have many superfluid phases. Unfortunately, however, there are only two phases realized ; BW-state(B-phase) and ABM-state(A-phase). Superfluid 3He-B is very sensitive against the solid wall. The perpendicular component of the wave function of with respect to the wall, which is denoted as Δ_〓(k), has a property of odd function near the wall. That is, Δ_〓(-k)=-Δ_〓(k). Due to this property, Δ_〓(k) gradually recovers to the bulk value as the distance from the wall increases with the characteristic length of several times of the coherence length ξ, whereasΔ_// exhibits no effect of the wall. ξ is typically several nanometers. As a result of this spatial variation of Δ_〓(k), there comes out the surface state inside the gap at the wall position. This surface state is called as "Andreev surface bound state", which is a typical feature of P-wave superfluid at the boundary. The property of the surface bound state crucially depends on the boundary condition at the wall. If the reflection of quasi-particles at the wall is diffusive(which is often the case with the ordinary wall), the bound state is not δ-function like, but has wider energy width. These surface properties of superfluid 3He-B is, of course, predicted by the theory, has not been studied experimentally yet. The reason is that we had no relevant probing techniques. In the present project, we succeeded in detecting this surface bound state, by the precise measurement of the acoustic shear motion of AC-cut quarts transducer with proper resonance frequencies. The signature of the surface bound state was detected as a kink of in the real part of the impedance and in the cusp of the imaginary part of it. The experimental result is well reproduced by the numerical calculation of the shear impedance by the Green function model.
  • ナノ多孔質中で進行するヘリウムの一次相転移の可視化
    ＣＯＥ２１「量子ナノ物理学」：
    Date (from‐to) : 2004
  • 超音波による固体ヘリウムの結晶成長融解の制御と新しい量子界面ダイナミクス
    住友財団：住友財団基礎科学研究助成
    Date (from‐to) : 2002/11 -2003/11
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    Date (from‐to) : 2001 -2002 
    Author : 野村 竜司
     
    収束超音波発振子を1K以下の極低温で一次元走査する機構を完成させ、超流動液体中の固体ヘリウム4の表面からの反射信号を観測した。反射信号の強度は強い温度依存性を示し、反射係数による結晶成長係数の測定が可能であると分かった。また一次元走査することによって得られた反射信号強度の界面と発振子間距離依存性(V(z)曲線と呼ばれる)の測定に成功した。これは界面での超音波反射係数の入射角依存性ひいては表面波の音速の情報を含むものである。固体ヘリウム4で初めてV(z)曲線の測定を行い、ラフニング転移温度以下でこれまでに知られていなかった非常に伝播速度の速い表面波励起が存在するらしいことが分かった。 また超音波を用いて自由に固体ヘリウム4を成長融解させることが可能であることを見出した。固液界面に超音波を放射すると、750mK以下の温度では超音波の方向に界面が力を受けて結晶が成長あるいは融解することを発見した。これは2次の音響効果である音響放射圧によって界面が力を受け、成長と融解が駆動されたとして定量的に説明できた。音響放射圧は古くから知られている概念であるが、これが結晶成長などの一次相転移を駆動できることは全く知られておらず、我々の実験ではじめて明らかになった。この放射圧による界面移動の温度依存性を測定するとラフな界面では800mK以上の高温で力の向きが音波の向きと逆になった。またこの逆転温度はファセットに近づくと急激に低下するなどの大きな異方性を持つことが分かった。 融解圧下にある液体中で超音波パルスを照射すると超音波発振子上に固体が核生成した。同様のことを固体中で行うと今度は液体の泡が核生成することが分かった。超音波は固体核と液体核の両方を"可逆的"に生成するという特異な結果が得られた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas (B)
    Date (from‐to) : 1998 -2000 
    Author : OKUDA Yuichi, NOMURA Ryuji
     
    In this project we have clarified that the temperature dependence of the surface tension of liquid 3He below 100 mK is almost quenched (flat between 0 and 100 mK) and also there is a very small peak around 100 mK. The experimental results were analyzed based on the assumption that the local entropy density picture is correct. The leading term of the temperature dependence of surface tension is T^2 and the very small coefficient of T^2 term is the result that the Fermi energy density near the surface becomes smaller than that of bulk liquid and then gets much bigger as the density decreases more. As the coefficient of T^2 becomes very small, the next higher order term becomes important. The next term should be dependent on the model of the strongly correlated Fermi-liquid (^3He). We adopted the Misawa's model which describes the liquid ^3He as the nearly meta-magnetic model. In this theory the next leading term is cT^4ln(T/T^*). By a suitable fitting, we could reproduce the small maximum observed in the experiment perfectly. Thus we could deduce some important information on liquid 3He from the precise measurement of surface tension in the low temperature. We also have made some progress in the experiment on zero sound reflection at the superfluid ^3He surface. Unfortunately we could not perform the experiment during the project period but the first experiment will be done pretty soon.

Social Contribution

  • 超低温・超伝導・超流動
    Date (from-to) : 2023/08/06
    Role : Lecturer
    Sponser, Organizer, Publisher  : 北海道大学
    Event, Program, Title : 北海道大学令和５年度オープンキャンパス体験講義

Media Coverage

  • Inchworm Driving of 4He Crystals in Superfluid
    Date : 2017/07
    Program, newspaper magazine: 科学新聞
    Paper
  • 固体ヘリウムの本来の形 無重力下で観察成功
    Date : 2013/02
    Program, newspaper magazine: 科学新聞
    第3423号1面 Paper
  • 多孔体中でのヘリウム量子結晶 極低温で雪崩的に成長
    Date : 2012/02
    Program, newspaper magazine: 科学新聞
    第3374号4面 Paper
  • マヨラナフェルミ粒子 超流動ヘリウム3表面で実現
    Date : 2011/01
    Program, newspaper magazine: 科学新聞
    第3324号 Paper
  • エアロジェルの液化ヘリウム吸蔵 2段階パターン発見
    Date : 2006/05
    Program, newspaper magazine: 日刊工業新聞
    2006月5月10日23面 Paper
  • 超流動ヘリウムに不思議な現象 超音波で高速結晶成長
    Date : 2006/02
    Program, newspaper magazine: 科学新聞
    第3084号4面 Paper

Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.