研究者データベース
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プロフィール情報
所属
学位
プロフィール情報
姓
野村, ノムラ名
竜司, リュウジID各種
200901011284712056
所属
業績リスト
研究キーワード
研究分野
経歴
- 2021年06月 - 現在 北海道大学 大学院工学研究院 教授
- 2022年09月 - 2022年09月 室蘭工業大学 大学院生産システム工学専攻 非常勤講師
- 2021年08月 - 2021年09月 電気通信大学大学院情報理工学研究科 非常勤講師
- 2016年04月 - 2021年05月 東京工業大学理学院 助教
- 2020年04月 - 2020年09月 明治大学大学院理工学研究科 兼任講師
- 2018年12月 - 2018年12月 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年04月 - 2016年03月 東京工業大学大学院理工学研究科物性物理学専攻 助教
- 2000年04月 - 2007年03月 東京工業大学理工学研究科物性物理学専攻 助手
- 1998年12月 - 2000年03月 Northwestern University research fellow
- 1996年 - 1997年 :日本学術振興会 特別研究員（ＤＣ）
学歴
委員歴
- 2023年03月 - 2025年03月 日本物理学会 第79～80期代議員
- 2024年04月 - 2024年09月 ⽇本物理学会2024年秋季⼤会 実⾏委員
- 2013年12月 - 2013年12月 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｣第4回領域研究会 組織委員
- 2008年11月 - 2009年10月 日本物理学会 領域６世話人
- 2008年08月 - 2008年08月 スーパークリーン特定・若手夏の学校 世話人代表
受賞
- 2023年12月 日本物理学会 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年08月 International Conference on Ultra Low Temperature Physics (ULT2022) Best poster award
Dripping character of superfluid 4He droplets受賞者: Keita Onodera - 2017年06月 The Physical Society of Japan JPSJ Editors’ Choice
J. Phys. Soc. Jpn. 86, 074603-1-5 (2017) - 2014年12月 Institute of Physics IOPselect
New J. Phys. 16, 113022-1-9 (2014) - 2013年09月 Low Temp. Phys. Editor's Picks in Low Temp. Phys.
Low Temp. Phys. 39, 780-785 (2013) - 2013年05月 The Physical Society of Japan J. Phys. Soc. Jpn., 2012 Highly Cited Article
J. Phys. Soc. Jpn. 80, 013602 (2011) - 2013年03月 日本物理学会 第18回日本物理学会論文賞
- 2012年12月 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年12月 The Physical Society of Japan JPSJ Editors’ Choice
J. Phys. Soc. Jpn. 80, 013602-1-4 (2011) - 2011年01月 The Physical Society of Japan JPSJ Editors’ Choice
J. Phys. Soc. Jpn. 80, 123601-1-4 (2011) - 2007年09月 日本物理学会 第一回日本物理学会若手奨励賞
- 2006年02月 The Physical Society of Japan JPSJ Editors’ Choice
J. Phys. Soc. Jpn. 75, 023601-1-4 (2006)
論文
- Ryuma Nagatomo, Keita Onodera, Shiro Kashimoto, Yuki Aoki, Ryuji NomuraJournal of the Physical Society of Japan 92 12 2023年12月15日 [査読有り][通常論文]
- Keita Onodera, Ryuma Nagatomo, Shiro Kashimoto, Ryuji NomuraJournal of the Physical Society of Japan 91 6 065005-1 - 065005-2 2022年05月27日 [査読有り][通常論文]
- Mutsuki Saito, Ryunosuke Takagishi, Nobuyuki Kurita, Masari Watanabe, Hidekazu Tanaka, Ryuji Nomura, Yoshiyuki Fukumoto, Kazuhiko Ikeuchi, Ryoichi KajimotoPhysical Review B 105 6 064424-1 - 064424-15 2022年02月17日 [査読有り]
- R. Nomura, Y. OkudaReviews of Modern Physics 92 4 2020年12月02日 [査読有り][招待有り]
- Crystallization Onset of Liquid Pockets via Mass Flow through Solid 4He in AerogelR. Nomura, H. Matsuda, Y. OkudaJ. Phys. Soc. Jpn. 88 035003-1 - 035003-2 2019年 [査読有り][通常論文]
- Crystallization of 4He in Aerogel with WarmingR. Nomura, H. Matsuda, Y. OkudaJ. Phys. Soc. Jpn. 87 115001-1 - 115001-2 2018年 [査読有り][通常論文]
- Taichi Yoshida, Akira Tachiki, Ryuji Nomura, Yuichi OkudaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 7 2017年07月 [査読有り][通常論文]
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 OkudaNew Journal of Physics 19 2 2017年02月01日 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 185 3-4 295 - 304 2016年11月 [査読有り][通常論文]
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. OkudaPHYSICAL REVIEW B 94 2 2016年07月 [査読有り][通常論文]
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. OkudaPHYSICAL REVIEW E 93 5 2016年05月 [査読有り][通常論文]
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 OkudaSCIENCE ADVANCES 1 9 2015年10月 [査読有り][通常論文]
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 OkudaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 84 6 2015年06月 [査読有り][通常論文]
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. NagaiPHYSICAL REVIEW LETTERS 114 10 2015年03月 [査読有り][通常論文]
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 OkudaNEW JOURNAL OF PHYSICS 16 2014年11月 [査読有り][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 175 1-2 120 - 125 2014年04月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 175 1-2 126 - 132 2014年04月 [査読有り][通常論文]
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 OkudaPHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 55 42 - 47 2014年01月 [査読有り][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS 39 9 780 - 785 2013年09月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 171 3-4 295 - 301 2013年05月 [査読有り][通常論文]
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. OkudaPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics 87 3 2013年03月15日 [査読有り][通常論文]
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 OkudaNEW JOURNAL OF PHYSICS 14 2012年12月 [査読有り][通常論文]
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. NomuraJOURNAL OF PHYSICS-CONDENSED MATTER 24 34 2012年08月 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW E 85 3 2012年03月 [査読有り][通常論文]
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. OkudaPHYSICAL REVIEW LETTERS 108 2 2012年01月 [査読有り][通常論文]
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. OkudaPHYSICAL REVIEW B 85 2 2012年01月 [査読有り][通常論文]
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 Okuda26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年 [査読有り][通常論文]
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. Okuda26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年 [査読有り][通常論文]
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 OkudaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 12 2011年12月 [査読有り][通常論文]
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 ShirronMICROGRAVITY SCIENCE AND TECHNOLOGY 23 4 365 - 372 2011年11月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 162 5-6 399 - 406 2011年03月 [査読有り][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 162 5-6 733 - 739 2011年03月 [査読有り][通常論文]
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 NagaiJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 1 2011年01月 [査読有り][通常論文]
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 OkudaPHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 43 3 718 - 721 2011年01月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 158 1-2 141 - 146 2010年01月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 158 1-2 268 - 274 2010年01月 [査読無し][通常論文]
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. NagaiPHYSICAL REVIEW LETTERS 103 15 155301 2009年10月 [査読無し][通常論文]
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. BurmistrovJOURNAL OF FLUID MECHANICS 619 261 - 275 2009年01月 [査読無し][通常論文]
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. Okuda25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 032064 2009年 [査読無し][通常論文]
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 Okuda25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 2009年 [査読有り][通常論文]
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. Nagai25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 2009年 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW B 78 21 214516 2008年12月 [査読無し][通常論文]
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 NomuraJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 11 111009-1-10 2008年11月 [査読無し][通常論文]
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 OkudaPHYSICAL REVIEW LETTERS 101 17 175703 2008年10月 [査読無し][通常論文]
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. - H. Abe, Y. Saitoh, T. Ueda, R. Nomura, Y. Okuda, S. N. BurmistrovLOW TEMPERATURE PHYSICS 34 4-5 308 - 311 2008年04月 [査読無し][通常論文]
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. BurmistrovLOW TEMPERATURE PHYSICS 34 4-5 308 - 311 2008年04月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 150 3-4 154 - 159 2008年02月 [査読有り][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 150 3-4 289 - 294 2008年02月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 150 3-4 499 - 504 2008年02月 [査読有り][通常論文]
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 HiroiJOURNAL OF LOW TEMPERATURE PHYSICS 149 3-4 143 - 150 2007年11月 [査読無し][通常論文]
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 OkudaPHYSICAL REVIEW E 76 4 2007年10月 [査読有り][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 148 5-6 553 - 557 2007年09月 [査読無し][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 148 5-6 621 - 625 2007年09月 [査読無し][通常論文]
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. OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 148 3-4 109 - 113 2007年08月 [査読無し][通常論文]
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. BurmistrovJOURNAL OF LOW TEMPERATURE PHYSICS 148 3-4 133 - 138 2007年08月 [査読無し][通常論文]
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. OkudaJETP LETTERS 85 11 581 - 584 2007年08月 [査読有り][通常論文]
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 Okuda12TH INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER (PHONONS 2007) 92 2007年 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW B 74 22 2006年12月 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW E 73 4 049901 2006年04月 [査読無し][通常論文]
- R Nomura, K Yoneyama, Y OkudaPHYSICAL REVIEW E 73 4 2006年04月 [査読有り][通常論文]
- R Nomura, W Miyashita, K Yoneyama, Y OkudaPHYSICAL REVIEW E 73 3 032601 2006年03月 [査読無し][通常論文]
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 ParshinJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 2 023601-1-4 2006年02月 [査読無し][通常論文]
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. OkudaAIP Conf. Proc., 24th International Conference on Low Temperature Physics 850 251 - + 2006年 [査読無し][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 89 - + 2006年 [査読無し][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 91 - + 2006年 [査読無し][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 145 - + 2006年 [査読無し][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 345 - + 2006年 [査読無し][通常論文]
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. OkudaJ. Jpn. Soc. Microgravity Appl. 23 3 134 - 138 日本マイクログラビティ応用学会 2006年 [査読無し][通常論文]
- W. Miyashita, K. Yoneyama, H. Kato, R. Nomura, Y. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 251 - + 2006年 [査読有り][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 145 - + 2006年 [査読有り][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 345 - + 2006年 [査読有り][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 91 - + 2006年 [査読有り][通常論文]
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. OkudaLOW TEMPERATURE PHYSICS, PTS A AND B 850 89 - + 2006年 [査読有り][通常論文]
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 OkudaJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 8-9 1509 - 1511 2005年08月 [査読無し][通常論文]
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 OkudaJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 8-9 1349 - 1351 2005年08月 [査読無し][通常論文]
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 OkudaJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 8-9 1467 - 1470 2005年08月 [査読無し][通常論文]
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, M. Yamamoto, Y Nagato, S. Higashitani, K. NagaiPhys. Rev. Lett 95 7 075301 2005年08月 [査読無し][通常論文]
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 OkudaPHYSICAL REVIEW B 71 21 214506-1-7 2005年06月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 138 3-4 835 - 840 2005年02月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 138 3-4 783 - 788 2005年02月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 138 3-4 893 - 898 2005年02月 [査読有り][通常論文]
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. OkudaPhysical Review B - Condensed Matter and Materials Physics 70 5 1 - 54516 2004年08月 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW B 70 5 054516-1-7 2004年08月 [査読無し][通常論文]
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 OkudaPHYSICAL REVIEW E 70 2 021606 2004年08月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 134 3-4 945 - 958 2004年02月 [査読有り][通常論文]
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 MicrogravityY. Okuda, R. Nomura日本マイクログラビティ応用学会誌 22 159 - 164 2004年
- K. Yoneyama, R. Nomura, Y. OkudaPhysical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 70 2 5 2004年 [査読有り][通常論文]
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. OkudaPhysica Status Solidi C: Conferences 1 11 3003 - 3006 2004年 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 134 1-2 157 - 162 2004年01月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 134 1-2 145 - 150 2004年01月 [査読無し][通常論文]
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 OkudaPHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL. 1, NO. 11 1 11 3003 - 3006 2004年 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 134 1-2 157 - 162 2004年01月 [査読有り][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 134 1-2 145 - 150 2004年01月 [査読有り][通常論文]
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 YamanakaJAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 8 5205 - 5207 2003年08月 [査読無し][通常論文]
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 YamanakaJAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 8 5205 - 5207 2003年08月 [査読有り][通常論文]
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, Y Suzuki, S Kimura, Y Okuda, S BurmistovLOW TEMPERATURE PHYSICS 29 6 492 - 494 2003年06月 [査読無し][通常論文]
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 BurmistrovPHYSICA B-CONDENSED MATTER 329 364 - 365 2003年05月 [査読無し][通常論文]
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 YamanakaPHYSICA B-CONDENSED MATTER 329 1664 - 1665 2003年05月 [査読無し][通常論文]
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 DaPHYSICA B-CONDENSED MATTER 329 116 - 117 2003年05月 [査読有り][通常論文]
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 OkudaPHYSICA B-CONDENSED MATTER 329 234 - 235 2003年05月 [査読有り][通常論文]
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 OkudaPHYSICAL REVIEW LETTERS 90 7 075301 2003年02月 [査読無し][通常論文]
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 OkudaPHYSICA B-CONDENSED MATTER 316 613 - 615 2002年05月 [査読無し][通常論文]
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 OkudaJOURNAL OF CRYSTAL GROWTH 237 47 - 50 2002年04月 [査読無し][通常論文]
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 OkudaJOURNAL OF LOW TEMPERATURE PHYSICS 126 1-2 39 - 44 2002年01月 [査読無し][通常論文]
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 HalperinPHYSICAL REVIEW LETTERS 87 3 035701 2001年07月 [査読無し][通常論文]
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 HalperinPHYSICAL REVIEW LETTERS 87 3 2001年07月 [査読有り][通常論文]
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, T.M. Haa, Y. Lee, N. Mulders, W.P. HalperinJ. Low Temp. Phys. Rapid Comunication 122 1-2 1 - 10 2001年01月 [査読無し][通常論文]
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 HalperinPHYSICAL REVIEW LETTERS 85 20 4325 - 4328 2000年11月 [査読無し][通常論文]
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 MizusakiPHYSICAL REVIEW LETTERS 85 14 2977 - 2980 2000年10月 [査読無し][通常論文]
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 HalperinPHYSICA B 284 289 - 290 2000年07月 [査読無し][通常論文]
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 MizusakiPHYSICA B 280 1-4 140 - 141 2000年05月 [査読有り][通常論文]
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 MizusakiJOURNAL OF LOW TEMPERATURE PHYSICS 113 5-6 763 - 768 1998年12月 [査読無し][通常論文]
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 MizusakiJOURNAL OF LOW TEMPERATURE PHYSICS 105 1-2 67 - 92 1996年10月 [査読無し][通常論文]
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 MizusakiJOURNAL OF LOW TEMPERATURE PHYSICS 105 1-2 67 - 92 1996年10月 [査読有り][通常論文]
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 MizusakiFIZIKA NIZKIKH TEMPERATUR 22 2 182 - 188 1996年02月 [査読無し][通常論文]
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 MizusakiFIZIKA NIZKIKH TEMPERATUR 22 2 182 - 188 1996年02月 [査読有り][通常論文]
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 MizusakiCZECHOSLOVAK JOURNAL OF PHYSICS 46 S6 2995 - 3002 1996年 [査読無し][通常論文]
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 MIZUSAKIJOURNAL OF LOW TEMPERATURE PHYSICS 94 5-6 377 - 383 1994年03月 [査読有り][通常論文]
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 HIRAIPHYSICA B 194 929 - 930 1994年02月 [査読有り][通常論文]
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 3HeT. Matsushita, R. Nomura, H.H. Hensley, K. Fukuda, T. Mizusaki A. HiraiPhysica B 194 901 - 902 1994年 [査読無し][通常論文]
- T MATSUSHITA, R NOMURA, K FUKUDA, T MIZUSAKI, A HIRAIJOURNAL OF LOW TEMPERATURE PHYSICS 89 1-2 365 - 373 1992年10月 [査読有り][通常論文]
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 Dripping of Superfluid DropletsK. Onodera, R. Nagatomo, K. Miyake, S. Kashimo, Y. Aoki, R. Nomura International Conference on Quantum Liquid Crystals 2023 (QLC2023) 2023年08月
- Quantized Dripping Period of Superfluid 4HeR. Nagatomo, K. Onodera, K. Miyake, S. Kashimoto, Y. Aoki, R. Nomura International Conference on Quantum Liquid Crystals 2023 (QLC2023) 2023年08月
- Robust quantization of dripping period for superfluid 4He dropletsR. Nomura, R. Nagatomo, K. Onodera, K. Miyake, S. Kashimoto, Y. Aoki 28th International Conference on Statistical Physics, Statphys28 2023年08月
- Dripping character of superfluid 4He dropletsK. Onodera, R. Nagatomo, S. Kashimoto, Y. Aoki, R. Nomura International Conference on Ultra Low Temperature Physics (ULT2022) 2022年08月 [査読無し][通常論文]
- Increasing the film flow rate of 4He by coatingK. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura International Conference on Ultra Low Temperature Physics (ULT2022) 2022年08月 [査読無し]
- Dripping Period of Superfluid 4He due to Film FlowR. Nagatomo, K. Onodera, S. Kashimoto, Y. Aoki, R. Nomura International Conference on Ultra Low Temperature Physics (ULT2022) 2022年08月 [査読無し][通常論文]
- Dripping Period of Superfluid 4He via Film FlowR. Nagatomo, K. Onodera, S. Kashimoto, R. Nomura 29th International Conference on Low Temperature Physics 2022年08月 [査読無し][通常論文]
- Enhancing the Film Flow of Superfluid 4He by CoatingK. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura 29th International Conference on Low Temperature Physics 2022年08月 [査読無し][通常論文]
- Falling Behavior of Superfluid 4He DropletsK. Onodera, R. Nagatomo, S. Kashimoto, R. Nomura 29th International Conference on Low Temperature Physics 2022年08月 [査読無し][通常論文]
- 上野 健一, 大澤 藍子, 三森 智弘, 加藤 晴子, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 63 (2) 709 -709 2008年08月25日
- 田村 雄太, 村川 智, 和田 雄一郎, 和才 将大, 斎藤 政通, 青木 悠樹, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 63 (2) 719 -719 2008年08月25日
- 和田 雄一郎, 西田 了平, 斎藤 政通, 青木 悠樹, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 60 (2) 669 -669 2005年08月19日
- 阿部 陽香, 斉藤 雄, 上田 哲人, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 60 (2) 666 -666 2005年08月19日
- 阿部 陽香, 小笠 原太, 斉藤 雄, 上田 哲人, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 60 (1) 764 -764 2005年03月04日
- 斎藤 政通, 青木 悠樹, 和田 雄一郎, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 60 (1) 763 -763 2005年03月04日
- 宮下 渉, 米山 圭一, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 59 (2) 714 -714 2004年08月25日
- 和田 雄一郎, 青木 悠樹, 荻野 篤, 谷口 二朗, 斎藤 政通, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 59 (2) 708 -708 2004年08月25日
- 小笠原 太, 木村 誠一郎, 多々良 辰哉, 阿部 陽香, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 59 (1) 822 -822 2004年03月03日
- 青木 悠樹, 和田 雄一郎, 荻野 篤, 斉藤 政通, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 59 (1) 815 -815 2004年03月03日
- 小笠原 太, 木村 誠一郎, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 58 (2) 693 -693 2003年08月15日
- 青木 悠樹, 関本 裕之, 和田 雄一郎, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 58 (1) 759 -759 2003年03月06日
- 青木 悠樹, 山口 航, 関本 裕之, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 56 (2) 640 -640 2001年09月03日
- 前川 道英, 鈴木 靖欣, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 56 (1) 728 -728 2001年03月09日
- 青木 悠樹, 山口 航, 野村 竜司, 松本 宏一, 奥田 雄一 日本物理学会講演概要集 56 (1) 720 -720 2001年03月09日
- 奥村 友志, 前川 道英, 野村 竜司, 奥田 雄一 日本物理学会講演概要集 55 (2) 670 -670 2000年09月10日
- 野村 竜司, 内田 昭嘉, 鈴木 雅史, ヘンスリー H.H., 佐々木 豊, 水崎 隆雄 日本物理学会講演概要集 52 (2) 615 -615 1997年09月16日
- 松下 琢, 野村 竜司, ヘンスリー H.H., 志賀 仁, 福田 耕治, 水崎 隆雄 日本物理学会講演概要集. 年会 50 (3) 434 -434 1995年03月16日
- Models for the Growth Mechanisms of Frost Heave in HeliumR. Nomura, T. Mizusaki 111 -120 1995年 [査読無し][通常論文]
- 松下 琢, 野村 竜司, ヘンスリー H.H., 福田 耕治, 水崎 隆雄, 平井 章 日本物理学会講演概要集. 年会 48 (3) 274 -274 1993年03月16日
- 松下 琢, 野村 竜司, 福田 耕治, 水崎 隆雄, 平井 章 年会講演予稿集 46 (3) 233 -233 1991年09月12日
書籍等出版物
- 超流動液体から生じる4He量子結晶の平衡形と非平衡形野村竜司, 奥田雄一
日本結晶成長学会誌 47巻4号 03-1-10（2020） 2020年 - 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年 - 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年 - 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年 - 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年 - 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年 - 固体４Ｈｅの結晶成長の新展開と航空機実験奥田雄一, 野村竜司
日本マイクログラビティ応用学会誌 vol. 24, No. 2, 183-187 (2007) 2007年 - 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年 - 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年 - 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年
講演・口頭発表等
- 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年12月 公開講演，セミナー，チュートリアル，講習，講義等
- Quantum Crystallizations of 4He Far from Equilibrium [招待講演]R. Nomura29th International Conference on Low Temperature Physics 2022年08月 口頭発表（基調）
- トポロジカル超流動ヘリウム3のヒッグスモードと表面マヨラナモード [招待講演]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年05月 公開講演，セミナー，チュートリアル，講習，講義等
- トポロジカル超流動3He-B相の表面マヨラナ状態の観測 [招待講演]ヘリウム・オンラインセミナー 第２７回 2021年12月 公開講演，セミナー，チュートリアル，講習，講義等
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- Falling of 4He Crystals in Superfluid [招待講演]R. Nomura, Y. OkudaQFS2021 International Online Conference 2021年08月 口頭発表（招待・特別）
- 平衡から大きく離れた固体4Heの結晶形 [招待講演]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年05月 公開講演，セミナー，チュートリアル，講習，講義等
- 超流動流の影響を受けた4He結晶の非平衡形 [招待講演]野村竜司ヘリウム・オンラインセミナー 2020年12月 公開講演，セミナー，チュートリアル，講習，講義等
- 平衡下および非平衡下における4Heの結晶形 [招待講演]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年12月 シンポジウム・ワークショップパネル（指名）
- 超流動3He-B相の表面マヨラナ励起 [招待講演]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年11月 口頭発表（招待・特別）
- Liquid Pocket Formation and Its Crystallization Onset via Mass Flow through Solid 4He in Aerogel [招待講演]R. Nomura, Y. OkudaInternational Conference on Quantum Fluids and Solids (QFS2019) 2019年08月 口頭発表（招待・特別）
- 機械振動子を用いたトポロジカル超流体研究の進展 [招待講演]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年03月 シンポジウム・ワークショップパネル（指名）
- Crystallization Dynamics of 4He in Aerogels [招待講演]R. Nomura12th International Conference on Cryocrystals and Quantum Crystals 2018年08月 口頭発表（招待・特別）
- Inchworm Driving of 4He Crystals in Superfluid [招待講演]R. Nomura, T. Yoshida, A. Tachiki, Y. OkudaInternational Symposium on Quantum Fluids and Solids 2018 2018年07月 口頭発表（招待・特別）
- トポロジカル超流動3Heの新奇準粒子状態 [招待講演]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年09月 シンポジウム・ワークショップパネル（指名）
- Crystallization dynamics of 4He far from equilibrium [招待講演]Ryuji NomuraULT 2017 Frontiers of Low Temperature Physics 2017年08月 口頭発表（基調）
- Anomalous Asymmetry in Melting and Growth Relaxations of 4He Crystals after Manipulation by Acoustic Radiation Pressure [通常講演]R. Nomura, H. Abe, Y. OkudaThe 28th International Conference on Low Temperature Physics 2017年08月 口頭発表（一般）
- 4He Crystals in Superfluid out of Equilibrium [招待講演]R. NomuraUniversity of Florida, Department of Physics, Colloquium 2017年03月 公開講演，セミナー，チュートリアル，講習，講義等
- Avalanche Crystallization of 4He in Aerogel [通常講演]R. Nomura, Y. OkudaAvalanches, plasticity, and nonlinear response in nonequilibrium solids 2016年03月 口頭発表（一般）
- 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 [招待講演]野村竜司金沢大学理学談話会 2015年12月 公開講演，セミナー，チュートリアル，講習，講義等
- 超流動3Heにおけるトポロジカル量子相転移の探索 [招待講演]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年12月 口頭発表（招待・特別）
- 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 [招待講演]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年09月 シンポジウム・ワークショップパネル（指名）
- Experimental Search for Majorana Fermion in 3He-B; Achievements and Challenges [招待講演]R. NomuraGrand Challenges in Quantum Fluids and Solids Workshop 2015年08月 シンポジウム・ワークショップパネル（指名）
- Magnetic Field Effects on the Surface Majorana Bound States of Superfluid 3He B-phase [招待講演]R. Nomura, M. Wasai, K. Akiyama, M. Mashino, T. Nakao, S. Murakawa, Y. OkudaInternational Conference on Topological Quantum Phenomena 口頭発表（招待・特別）
- Magnetic field effects on surface Majorana fermions of superfluid 3He-B [通常講演]R. Nomura, M. Wasai, K. Akiyama, M. Mashino, T. Nakao, S. Murakawa, Y. Okuda27th International Conference on Low Temperature Physics (LT27) 2014年08月 口頭発表（一般）
- 4Heの結晶成長；その普遍性と特異性 [招待講演]野村竜司東工大物性セミナー 2014年06月 公開講演，セミナー，チュートリアル，講習，講義等
- 乱れの下で進行する量子固体の結晶化 [招待講演]京都大学物理学第一教室佐々研究室セミナー 2013年09月 公開講演，セミナー，チュートリアル，講習，講義等
- Self-organized criticality in quantum crystallization of 4He in aerogel [招待講演]R. Nomura, H. Matsuda, A. Ochi, R. Isozaki, Y. OkudaInternational Conference on Quantum Fluids and Solids (QFS2013) 2013年08月 口頭発表（招待・特別）
- Power Law Behavior in Quantum Crystallization of 4He in Aerogel [通常講演]R. Nomura, H. Matsuda, A. Ochi, R. Isozaki, Y. OkudaSTATPHYS25, the 25th International Conference on Statistical Physics 2013年07月 口頭発表（一般）
- Surface Majorana cone of the topological superfluid 3He B phase [招待講演]R. NomuraAPS March Meeting 2013, Invited Session: Superfluids under Nanoscale Confinement 2013年03月 口頭発表（招待・特別）
- Surface Majorana Cone of the Topological Superfluid 3He B Phase [招待講演]R. NomuraInternational Conference on Topological Quantum Phenomena 2012年05月 口頭発表（招待・特別）
- Andreev-Majorana bound states on the superfluid 3He-B surface [招待講演]R. NomuraMicrokelvin workshop 2012 2012年03月 シンポジウム・ワークショップパネル（指名）
- Surface Majorana Cone of the Superfluid 3He B Phase [招待講演]R. NomuraInternational Workshop for Young Researchers on Topological Quantum Phenomena 2011年11月 シンポジウム・ワークショップパネル（指名）
- Surface Majorana Cone of the Superfluid 3He B Phase [招待講演]R. NomuraULT2011, the new frontiers of low temperature physics 2011年08月 口頭発表（招待・特別）
- 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 [招待講演]野村竜司東京大学物性研究所セミナー 2011年07月 公開講演，セミナー，チュートリアル，講習，講義等
- 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 [招待講演]野村竜司青山学院大学 物理・数理学科コロキウム 2011年06月 公開講演，セミナー，チュートリアル，講習，講義等
- 超音波で探る固体４Heの結晶成長・超流動３Heの表面状態 [招待講演]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年10月 シンポジウム・ワークショップパネル（指名）
- Surface Andreev Bound States and Surface Majorana Fermions on the Superfluid 3He B Phase [招待講演]R. NomuraUniversity of Florida, Department of Physics, Seminar 2010年03月 公開講演，セミナー，チュートリアル，講習，講義等
- Thermal and quantum crystallizations of 4He in aerogel [通常講演]R. Nomura, R. Masumoto, K. Ueno, Y. OkudaAPS March Meeting 2010年03月 口頭発表（一般）
- Surface Andreev Bound States and Surface Majorana States on the Superfluid 3He B Phase [通常講演]R. Nomura, S. Murakawa, Y. Wada, M. Wasai, K. Akiyama, Y. Tamura, M. Saitoh, Y. Aoki, Y. OkudaInternational Symposium on Physics of New Quantum Phases in Superclean Materials 2010年03月 口頭発表（一般）
- Surface Andreev Bound States in Superfluid 3He-B [招待講演]R. Nomura, S. Murakawa, Y. Wada, M. Wasai, K. Akiyama, Y. Tamura, M. Saitoh, Y. Aoki, Y. OkudaInternational Symposium on Novel Spin Pairing 2009 (NSP2009) 2009年09月 シンポジウム・ワークショップパネル（指名）
- 量子固体の結晶成長 [招待講演]野村竜司物性物理夏の学校 サブゼミ 公開講演，セミナー，チュートリアル，講習，講義等
- ヘリウムの結晶成長；その普遍性と特異性 [招待講演]野村竜司スーパークリーン特定・若手夏の学校 2008年08月 公開講演，セミナー，チュートリアル，講習，講義等
- Surface Andreev bound states of superfluid 3He on a specularity-controlled wall [通常講演]R. Nomura, S. Murakawa, Y. Wada, Y. Tamura, M. Saitoh, Y. Aoki, Y. Okuda, Y. Nagato, M. Yamamoto, S. Higashitani, K. Nagai25th international conference on Low Temperature Physics (LT25) 2008年08月 口頭発表（一般）
- 超流動体から生じるヘリウム結晶の特異な成長過程 [招待講演]野村竜司東工大宇宙物理学理論研究室セミナー 2008年06月 公開講演，セミナー，チュートリアル，講習，講義等
- 平衡から大きく外れた４Ｈｅ結晶 [招待講演]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年09月 口頭発表（招待・特別）
- Avalanche growth of 4He crystals in aerogels [通常講演]R. Nomura, A. Osawa, T. Mimori, H. Kato, Y. OkudaThe International Conference on Science of Friction 2007年09月 口頭発表（一般）
- Dynamical Phase Transition of 4He Crystals in Aerogels [通常講演]Ryuji Nomura, Haruko Kato, Aiko Osawa, Yuichi OkudaPhysics of superclean materials International Workshop “Physics of Supersolids and Related Topics” 2007年04月 口頭発表（一般）
- 音響放射圧によるヘリウムの結晶成長 [招待講演]野村竜司東大駒場物性セミナー 2006年12月 公開講演，セミナー，チュートリアル，講習，講義等
- Transverse Acoustic Impedance of Superfluid 3He and Surface Andreev Bound States [招待講演]R. Nomura, Y. Wada, R. Nishida, M. Saitoh, Y. Aoki, S. Murakawa, Y. OkudaInternational symposium on quantum fluids and solids 2006年08月 シンポジウム・ワークショップパネル（指名）
- Anisotropic Interface Motion of 4He Crystal in an Acoustic Field [通常講演]R. Nomura, F. Ogasawara, Y. Saitoh, H. Abe, Y. OkudaTodai International Symposium 2004 and The Ninth ISSP International Symposium on Quantum Condensed System 2004年11月 口頭発表（一般）
- High-Speed Dynamics in Largely Deformed Crystal-Superfluid Interface of 4He [通常講演]R. Nomura, F. Ogasawara, Y. Saitoh, H. Abe, Y. OkudaVortex and Turbulence in Classical and Quantum Fluids 2004年10月 口頭発表（一般）
- Nucleation and Growth of 4He Crystal by Acoustic Radiation Pressure [招待講演]R. NomuraWorkshop on Ultra-low Temperature Physics (ULT) 2002年08月 口頭発表（招待・特別）
- エアロジェル中３Heの超音波測定 [招待講演]野村竜司日本物理学会第５６回年会 2001年03月 口頭発表（招待・特別）
- 超流動３Heにおける不純物効果 Dirty Superfluid [招待講演]野村竜司東工大物性セミナー 2000年06月 公開講演，セミナー，チュートリアル，講習，講義等
所属学協会
共同研究・競争的資金等の研究課題
- 日本学術振興会：科学研究費助成事業 基盤研究(C)研究期間 : 2017年04月 -2021年03月代表者 : 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)研究期間 : 2016年04月 -2018年03月代表者 : 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。
- 日本学術振興会：科学研究費助成事業 基盤研究(B)研究期間 : 2014年04月 -2018年03月代表者 : 野村 竜司, 奥田 雄一圧電素子で基板を左右へ非対称なずれ振動させることにより、動摩擦と静摩擦の差を利用して、超流動4He中に水平に配した基板上の4He結晶を水平方向に駆動することに初めて成功した。観測された4He結晶の運動は、通常物質の運動と大きく異なり、高速で超流動体から結晶成長する4He結晶の量子性が関わった新しいタイプの駆動様式によるものであった。 また超流動液体中の4He結晶の濡れ性の制御が、基板の粗面化により可能であることを実証した。これにより、結晶においても、基板表面に液体が浸潤するCassie-Baxter状態がありえることが示された。
- Investigating Spin Degrees of Freedom of Surface Andreev Bound States of Non-unitary Superfluid Helium Three in High Magnetic FieldsNational High Magnetic Field Laboratory：User Program研究期間 : 2017年
- 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)研究期間 : 2010年04月 -2016年03月代表者 : 前野 悦輝, 田仲 由喜夫, 石川 修六, 鄭 国慶, 柏谷 聡, 浅野 泰寛, 野村 竜司, 安藤 陽一, 佐藤 昌利, 上田 正仁, 野村 竜司, 佐藤 昌利, 田仲 由喜夫, 浅野 泰寛, 上田 正仁平成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。 - 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)研究期間 : 2010年04月 -2015年03月代表者 : 石川 修六, 野村 竜司, 東谷 誠二, 三宅 和正, 高木 丈夫, 中原 幹夫, 池上 弘樹, 小原 顕, 松本 宏一, 竹内 宏光, 久保田 実超流動３Heには、時間反転対称性が破れたA相と軌道スピン対称性が破れたB相の２つの相がある。界面・境界面で示すトポロジカル量子現象を探求し、以下の成果を得た。A相での巨視的固有軌道角運動量の存在とB相での表面束縛状態のマヨラナコーンの存在を初めて示した。A相カイラリティの局所的な観測に成功した。B相での表面アンドレーエフ束縛状態のゼロエネルギー表面状態密度と奇周波数対振幅とが厳密に対応することを理論的に導くことに成功した。遅延効果をもつペアリング相互作用を取り入れ、マイスナー効果を示すバルクな奇周波数超伝導体が存在できることを理論的に確立した。
- 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研究期間 : 2014年03月
- 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研究期間 : 2012年12月
- 日本学術振興会：科学研究費助成事業 基盤研究(B)研究期間 : 2010年 -2012年代表者 : 奥田 雄一, 野村 竜司超流動3He-B相は、壁近傍ではユニークな準粒子状態をギャップ内に低エネルギー状態として持つ。我々は横波音響インピーダンスの手法により、その存在を確かめることに成功していた。さらに、壁表面を超流動4Heの薄膜で覆い、3He準粒子の散乱条件を変化させることで、その詳細を明らかにした。この表面束縛状態は、specularの極限でMajoranafermionになるという驚くべき結果が導かれ、その磁気的性質を解明している。
- International Workshop for Young Researchers on Topological Quantum Phenomena in Condensed Matter with Broken SymmetriesAsia Pacific Center for Theoretical Physics：External Activity for the Asia Pacific Center for Theoretical Physics, 2011研究期間 : 2011年11月
- 日本学術振興会：科学研究費助成事業 基盤研究(B)研究期間 : 2009年 -2011年代表者 : 野村 竜司, 奥田 雄一音響放射圧によって微小重力中のヘリウム4結品を駆動し、超流動ヘリウム中に浮遊させることに成功した。ピエゾ素子を用いたインチワーム駆動法で、ヘリウム結品中にステンレス試料が埋もれた状況下でも、ステンレス試料を動かすことに成功した。ピエゾ素子の極低温高圧下での動作に問題ないことが確認され、ヘリウム結晶への適用へあと一歩のところまでこぎっけた。エアロジェル中でのヘリウムの結晶化を調べ、量子トンネリングによる自己組織化臨界状態を見出した。
- 日本学術振興会：科学研究費助成事業 特定領域研究研究期間 : 2008年 -2009年代表者 : 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。
- 日本学術振興会：科学研究費助成事業 基盤研究(C)研究期間 : 2007年 -2008年代表者 : 野村 竜司, 奥田 雄一超流動ヘリウム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研究期間 : 2005年 -2007年
- 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研究期間 : 2007年01月
- 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研究期間 : 2006年
- 日本学術振興会：科学研究費助成事業 基盤研究(B)研究期間 : 2003年 -2005年代表者 : 野村 竜司, 奥田 雄一これまでに超音波を用いてヘリウム4結晶の成長、融解、核生成を駆動できることを報告してきた。これは2次の音響効果である音響放射圧によって1次相転移が駆動できることを示した最初の例である。最近我々はヘリウム4結晶の微斜面に固体側から超音波を照射すると上部にファセット面が現れて成長することを見出した。ファセットの成長速度は400mK以下で増加を止め一定値に飽和するが、その値は駆動力に比例した。この様な振る舞いは過去に測定されたステップの易動度をもとにした螺旋成長モデルでは全く説明できないものである。螺旋成長モデルでは、成長速度は低温で増大し続けまた駆動力の二乗に比例しなければなら無い。なによりもその絶対値が3桁以上小さくなってしまい、全く別の成長機構を考えることが必要となった。 超音波の一次の圧力振動は400mK以下でステップの速度を音速程度まで加速することが出来る。通常の結晶成長の常識では対面するステップが衝突すると対消滅し、ステップ密度は際限なくは増加しない。しかしこの様な高速ステップの衝突過程では、液体の慣性によってお互いに乗り上げて新たな層を形成しステップの増殖が進むという理論が最近パーシンとツィンバレンコによって発表された。この理論を基に成長モデル立てたところ実験結果を定量的に再現することが分かった。高速のステップ運動と超流体の運動が結合した量子固体ならでわの全く新しい結晶成長機構を発見した。
- 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研究期間 : 2005年
- 日本学術振興会：科学研究費助成事業 萌芽研究研究期間 : 2003年 -2004年代表者 : 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。
- 日本学術振興会：科学研究費助成事業 基盤研究(B)研究期間 : 2002年 -2004年代表者 : 奥田 雄一, 野村 竜司超流動3Heはスピン・トリプレットのP波超流動状態に約1〜2mKで相転移する。秩序変数の超流動の波動関数は多くの自由度を有しており、多数の超流動相の実現が原理的に可能と言われている。しかし、不思議なことに現実にはBW-state(B相)とABM-state(A相)の二つ、磁場中でABMの変形であるA1相が実現しているのみである。この中で固体界面という境界条件に敏感なのは、BW-stateである。BW-stateでは、超流動の波動関数の壁に垂直な成分Δ_⊥(k)は、壁近傍で奇関数的に振舞う。すなわちΔ_⊥(-k)=-Δ_⊥(k)という性質をもつ。その結果、Δ_は壁の影響をほとんど受けないが、Δ_⊥は壁からξの数倍にわたってバルクの値から大きく空間変化し、壁の直上でゼロになる。ここでξはコヒーレンス長で数十ナノメータの長さである。このように秩序変数が空間変化することのために、壁近傍ではP波超流動固有の表面状態が存在する。つまりギャップ内に状態密度を持つことになる。界面の条件が準粒子の衝突に対して鏡面的か非鏡面的かによって大きく変わるが、現実の系では非鏡面的であることを考慮すると、ギャップ内の状態がδ関数的ではなく、かなり幅を持って存在するところが特徴的である。これらのことは理論的にこそ予測されていたが、実験では技術上の問題で手付かずの状態になっていた。本研究において、壁の横振動の音響インピーダンスを適当な振動数を選んで精密に測定することにより、この表面状態の存在を明瞭に捕らえることができた。これは、実験前ではまったく予想しなかったことであるが、音響インピーダンスの手法が超流動3Heの表面状態の分光学的研究に有力であることを示しており、今後のこの分野の研究が進展することが期待される
- 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」：研究期間 : 2004年
- 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研究期間 : 2002年11月 -2003年11月
- 日本学術振興会：科学研究費助成事業 若手研究(B)研究期間 : 2001年 -2002年代表者 : 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。
- 日本学術振興会：科学研究費助成事業 特定領域研究(B)研究期間 : 1998年 -2000年代表者 : 奥田 雄一, 野村 竜司, 松本 宏一液体3Heの常流動相における表面張力の温度依存性が150mK以下の低温での測定は温度変化は非常に小さいことに加えて、100mK付近に小さいながら紛れもなくピークがあることがわかった。さらに三沢の理論を用いることで、小さなピークを説明をすることが出来た。それらは、現在論文にまとめる作業中である。 以上をまとめると、次のようになる。 1.液体^3He自由表面近傍で、密度が急激に変化しているところは、局所エントロピーの考えが成り立つとしてよい。 2.フェルミ縮退している領域で、表面張力の温度依存性を示す最初の項はT^2であるが、相反する効果のためその係数はほとんどゼロになる。温度依存性が100mK以下で極めて小さいことに対応している。 3.相反する効果の意味は、次のようなものである。密度が急激に小さくなるところで、フェルミエネルギー密度がバルクの値よりも一旦小さくなった後、急激に大きくなるために、T^2の係数は限りなくゼロに近くなる。 4.T^2の項が極めて小さいとさらにその次の項が効いてくる。その次の項の関数形は強く相互作用する^3Heの磁気モデルに敏感になってくるが、ここでは三沢理論によって(nearly metaganetic modelに近い)T^4ln(T/T*)の項を取り入れた。T*がフィッティングパラメータになるが、実験結果を見事に再現する事ができた。 5.以上、表面張力の精密測定から、液体3Heの磁気モデルについての重要な指針が得られた。 その他、ゼロ音波による超流動3He表面での実験の準備が進み、来年度早々に実験に入れる体勢が整った。 さらに、本計画研究で購入された希釈冷凍機が順調に運転されることが確認され、本格実験がスタート出来ることになった。
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