Nago, Yusuke



Faculty of Science and Technology, Department of Physics (Yagami)


Research Associate/Assistant Professor/Instructor

Other Affiliation 【 Display / hide

  • 東京大学 低温科学研究センター, 村川研究室, 客員共同研究員

Career 【 Display / hide

  • 2011.10

    大阪市立大学, 理学研究科, 特任助教

  • 2013.04

    東京理科大学, 理学部応用物理学科, 嘱託助教

  • 2014.06

    理化学研究所, 創発物性科学研究センター 量子情報エレクトロニクス部門 量子凝縮相研究チーム, 客員研究員


Research Areas 【 Display / hide

  • Condensed matter physics II

Research Keywords 【 Display / hide

  • Superfluidity、Superconductivity


Papers 【 Display / hide

  • Multiple Diffusion-Freezing Mechanisms in Molecular-Hydrogen Films

    Makiuchi T., Yamashita K., Tagai M., Nago Y., Shirahama K.

    Physical Review Letters (Physical Review Letters)  123 ( 24 )  2019.12

    ISSN  00319007

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    © 2019 American Physical Society. Molecular hydrogen is a fascinating candidate for novel bosonic and fermionic superfluids. We have studied diffusion dynamics of thin films of H2, HD, and D2 adsorbed on a glass substrate by measurements of elasticity. The elasticity shows multiple anomalies well below the bulk triple point temperature. They are attributed to three different diffusion mechanisms of admolecules and their "freezing" into a localized state: Classical thermal diffusion of vacancies, quantum tunneling of vacancies, and diffusion of molecules in the uppermost surface. The surface diffusion is active down to 1 K, below which the molecules become localized. This suggests that the surface layer of hydrogen films is on the verge of quantum phase transition to a superfluid state.

  • Elastic Anomaly of Thin Neon Film

    Makiuchi Takahiko, Yamashita Katsuyuki, Tagai Michihiro, Nago Yusuke, Shirahama Keiya

    Journal of the Physical Society of Japan (Physical Society of Japan)  88 ( 3 ) 34601 - 34601 2019

    Joint Work, Except for reviews,  ISSN  00319015

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    © 2019 The Physical Society of Japan. Adsorbed molecular films provide two-dimensional systems that show various emergent phenomena that are not observed in bulk counterparts. We have measured the elasticity of thin neon films adsorbed on porous glass down to 1 K by the torsional oscillator technique. The shear modulus of a neon film anomalously increases at low temperatures with excess dissipation. This behavior indicates a crossover from a soft (fluidlike) state at high temperatures to a stiff (solidlike) state at low temperatures. The temperature dependence of the anomaly is qualitatively similar to that of the elastic anomaly of helium films found in our recent study. The dissipation peak temperature, however, becomes constant at about 5 K, contrary to the case of helium, in which it decreases to 0 K at a critical coverage of a quantum phase transition between a gapped localized phase and a mobile (superfluid) phase. It is concluded that neon films behave as a classical system that does not show a quantum phase transition or superfluidity, although the films may be strongly supercooled to temperatures much lower than the bulk triple point, 24.6 K. Our results suggest that the elastic anomaly is a universal phenomenon of atomic or molecular films adsorbed on disordered substrates.

  • Elastic anomaly of helium films at a quantum phase transition

    Makiuchi T, Tagai M, Nago Y, Takahashi D, Shirahama K

    Physical Review B (Physical Review B)  98 ( 23 )  2018.12

    Joint Work, Except for reviews,  ISSN  24699950

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    © 2018 American Physical Society. Helium films show various quantum phases that undergo quantum phase transitions by changing coverage n. We found anomalous elastic phenomena in bosonic He4 and fermionic He3 films adsorbed on a glass substrate. The films stiffen under ac strain at low temperature with an excess dissipation. The onset temperature of the stiffening decreases to 0 K as n approaches a critical coverage nc. The elastic anomaly is explained by thermal activation of helium atoms from the localized to extended states with a distributed energy gap. We determine the energy band structure of helium films from elasticity. The ground states of He4 and He3 at n<nc, which are possibly a sort of Mott insulator or Mott glass, are identically gapped and compressible.

  • Magnetization measurements of Sr<inf>2</inf>RuO<inf>4</inf>-Ru eutectic microplates using dc-SQUIDs

    Nago Y., Sakuma D., Ishiguro R., Kashiwaya S., Nomura S., Kono K., Maeno Y., Takayanagi H.

    Journal of Physics: Conference Series (Journal of Physics: Conference Series)  969 ( 1 )  2018.04

    Research paper (international conference proceedings), Joint Work, Except for reviews,  ISSN  17426588

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    © Published under licence by IOP Publishing Ltd. We report magnetization measurements of Sr2RuO4-Ru eutectic microplates using micro-dc-SQUIDs. Sr2RuO4 is considered as a chiral p-wave superconductor and hence Sr2RuO4-Ru eutectic becomes in an unstable state with a superconducting phase frustration between a chiral p-wave state of Sr2RuO4 and a s-wave state of Ru. To compensate the frustration, a single quantum vortex is spontaneously formed at the center of the Ru inclusion at sufficiently low temperatures. However, such a spontaneous vortex state has not been experimentally observed yet. In this study, we prepared a micro-dc-SQUID and a Sr2RuO4-Ru eutectic microplate containing a single Ru-inclusion at the center of the microplate. We performed magnetization measurements down below the superconducting transition temperature of the Ru inclusion to investigate the spontaneous Ru-center vortex state.

  • Elasticity measurement of hydrogen film adsorbed on porous glass

    Makiuchi Takahiko, Yamashita Katsuyuki, Tagai Michihiro, Nago Yusuke, Takahashi Daisuke, Shirahama Keiya

    Meeting Abstracts of the Physical Society of Japan (The Physical Society of Japan)  73 ( 0 ) 1692 - 1692 2018

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Papers, etc., Registered in KOARA 【 Display / hide

Presentations 【 Display / hide

  • 六方晶窒化ホウ素表面上ヘリウム4薄膜の超流動と弾性


    日本物理学会第2020年秋季大会 (オンライン) , 2020.09, Oral Presentation(general)

  • ナノ多孔体Gelsil中ヘリウム4の流れ特性と超流動臨界指数

    谷智行,永合祐輔,村川智 ,白濱圭也

    日本物理学会第2020年秋季大会 (オンライン) , 2020.09, Oral Presentation(general)

  • 弾性異常で見たグラファイト上 4He 薄膜の量子相転移


    日本物理学会第2020年秋季大会 (オンライン) , 2020.09, Oral Presentation(general)

  • グラファイト上4He薄膜の弾性異常

    鈴木貴博 ,巻内崇彦,永合祐輔,白濱圭也

    日本物理学会第75回年次大会 (オンライン) , 2020.03, Oral Presentation(general)

  • グラファイト上4He薄膜の弾性効果

    鈴木貴博 ,巻内崇彦,永合祐輔,白濱圭也

    日本物理学会第2019年秋季大会 (岐阜大学柳戸キャンパス) , 2019.09, Oral Presentation(general)

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Research Projects of Competitive Funds, etc. 【 Display / hide

  • Novel Quantum Phenomena in 2D Helium with Aspects of Quantum Phase Transition


    Keio University, 白濱 圭也, 永合 祐輔, Grant-in-Aid for Scientific Research (A)

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  • Realization of Superfluidity in Adsorbed Molecular Films by Phonon Irradiation


    Keio University, 白濱 圭也, 石黒 亮輔, 永合 祐輔, Challenging Research (Exploratory)

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  • Elucidation of microscopic dynamics of quantum vortex in superfluid helium


    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research, Yusuke Nago, Grant-in-Aid for Early-Career Scientists, Research grant, Principal Investigator

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    超流動ヘリウム中でのscNWの機械共振テストを行うため、冷凍機および配線回路の準備を行った。真鍮製のハーメチックコネクタ付フィードスルーを作製し、冷凍機内に同軸配線を増築した。また、試料台を設計・金属加工作製し、超伝導細線振動子と音叉型水晶振動子を準備した。これらの振動子は、ヘリウム液面計、配線回路や印加磁場中の動作チェック、および本実験における量子渦生成装置として用いる。液中で生成した渦環がscNWまで到達して検出できるように、各振動子とscNW基板を互いの間隔を微調整して試料台上に配置した。試料を冷凍機で温度1.3K まで冷却し、購入した高周波ロックインアンプを用いて真空中および液体ヘリウム中で各振動装置の動作テストを行った。ナノワイヤー共振器については、磁場の有無で信号の相違を観測したが、現在のところ機械共振信号の確証までは至っていない。超伝導細線振動子と音叉型水晶振動子においては正常動作確認し、液体の粘性抵抗の温度依存性および超流動転移の観測に成功した。

  • Study of Quantum Vortex States in Spin-triplet Chiral p-wave Superconductor


    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research, Yusuke Nago, SAKUMA Daisuke, SHINOZAKI Tomoya, SATO Taichi, Grant-in-Aid for Young Scientists (B), Research grant, Principal Investigator

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    We developed magnetization measurement devices composed of micro dc-SQUIDs and Sr2RuO4(SRO) microplates for clarification of novel quantum vortex states attributable to spin-triplet chiral p-wave superconductivity, and obtained the experimental results as follows.
    1.Two distinct signals of the vortices implying influence of chiral superconductivity were obtained. 2. In the magnetization measurements under the in-plane magnetic field, the vortex signal implying a half-quantum vortex was detected. 3. In the magnetization measurements of SRO-Ru eutectic microplates, spatial distribution change of induced magnetic flux due to the superconducting transition of Ru was observed. However, spontaneous nucleation of vortex attributable to the phase competition between s-wave and chiral p-wave superconductivities was not observed.

  • Anomalous Magnetization induced Chiral edge currents of a Mesoscopic Chiral Superconducting Sr2RuO4 on Micro-dc-SQUIDs


    The Institute of Physical and Chemical Research, ISHIGURO Ryosuke, KASHIWAYA Hiromi, KASHIWAYA Satoshi, NAGO Yusuke, SAKUMA Daisuke, TANO Yusuke, SHINOZAKI Tomoya, Grant-in-Aid for Scientific Research (C)

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    We have developed new local magnetic field measurement system using SQUIDs (Al tunnel junction, Nb weak link, and FIB-CVD W type) in this study. We have tried to observe the chiral edge currents, using this system, to prove experimentally that Sr2RuO4 is a chiral P wave spin triplet superconductor.
    However, chiral edge currents, etc., phenomenons that show clearly chiral superconductivity has not been observed.

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Awards 【 Display / hide

  • 領域6若手奨励賞受賞

    永合 祐輔, 2018.03, 日本物理学会, 超流動ヘリウムにおける量子渦・量子乱流発生機構の実験的解明

    Type of Award: Awards of National Conference, Council and Symposium.  Country: 日本

  • 第10回低温工学・超伝導若手合同講演会信貴賞

    永合祐輔, 2011.12, 低温工学協会, 超微細超伝導線振動子による超流動ヘリウム中の量子渦検出

    Type of Award: Awards of National Conference, Council and Symposium.  Country: 日本

Other 【 Display / hide

  • 振動物体を用いた超流動ヘリウム中量子渦・量子乱流生成


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    大阪市立大学 2017年度 物理教室年末研究発表会 招待講演


Courses Taught 【 Display / hide











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Courses Previously Taught 【 Display / hide

  • 物理学実験第1

    Keio University, 2018, Spring Semester, Major subject, Laboratory work/practical work/exercise, Within own faculty, 6h

  • 物理学D演習

    Keio University, 2018, Autumn Semester, General education subject, Seminar, Within own faculty, 2h

  • 物理学実験第2

    Keio University, 2018, Autumn Semester, Major subject, Laboratory work/practical work/exercise, Within own faculty, 6h

  • 自然科学実験

    Keio University, 2018, Spring Semester, General education subject, Laboratory work/practical work/exercise, Within own faculty, 3h

  • 物理学実験第2

    Keio University, 2017, Autumn Semester, Major subject, Laboratory work/practical work/exercise, Within own faculty, 6h

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Social Activities 【 Display / hide

  • 絶対零度の世界~超伝導の不思議~

    慶應義塾大学, 2019年度 塾内高校生のための夏休み研究体験  (慶應義塾大学矢上キャンパス)

  • 超低温物理の世界:超流動と超伝導

    慶應義塾大学, 慶應義塾大学オープンキャンパス 一般向け講演 学問のすゝめ (慶應義塾大学矢上キャンパス)


Memberships in Academic Societies 【 Display / hide

  • 公益社団法人 応用物理学会, 

  • 一般社団法人 日本物理学会, 


Committee Experiences 【 Display / hide

  • 2019.10