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

  • 4D-XY Superfluid Transition and Dissipation in <sup>4</sup>He Confined in Nanoporous Media

    Tani T., Nago Y., Murakawa S., Shirahama K.

    Journal of the Physical Society of Japan (Journal of the Physical Society of Japan)  91 ( 1 )  2022.01

    ISSN  00319015

     View Summary

    4He confined in nanoporous Gelsil glass is a unique, strongly correlated Bose system exhibiting quantum phase transition (QPT) by controlling pressure. Previous studies revealed that the QPT occurs with four-dimensional (4D) XY criticality, which appears in the zero-temperature limit of the superfluid density. However, the P-T phase diagram also suggested that the 4D XY nature appears at finite temperatures. Here, we have determined the critical exponent of the superfluid density ρsof 4He in two Gelsil samples that have pore diameter to be about 3 nm, using a newly developed mechanical resonator technique. The critical exponent ζ in the powerlaw fitting ρsα |1 - T=Tc|ζ, where Tcis the superfluid transition temperature, was found to be 1.0 ± 0.1 for all pressures realized in this experiment, 0.1 > P > 2.4 MPa. This value of ζ gives decisive evidence that the finite-temperature superfluid transition belongs to the 4D XY universality class. The emergence of the 4D XY criticality is explained by the existence of many nanoscale superfluid droplets, the so-called localized Bose-Einstein condensates (LBECs), above Tc. Due to the large energy cost for 4He atoms to move between the LBECs, the phase of the LBEC order parameters fluctuates not only in spatial (3D) but imaginary time (+1D) dimensions, resulting in the 4D XY criticality by a temperature near Tc. Since the finite size of the system in the imaginary time dimension Ltis larger than the pore size, the 4D XY critical phenomenon is observed. In the very vicinity of Tcat which the correlation length exceeds Lt, there may be a crossover from 4D to 3D XY criticality. Below Tc, macroscopic superfluidity grows in the nanopores of Gelsil by the alignment of the phases of the LBEC order parameters. An excess dissipation peak observed below Tc is well explained by this phase-matching process.

  • 4D-XY Superfluid Transition and Dissipation in 4He Confined in Nanoporous Media

    Tomoyuki Tani, Yusuke Nago, Satoshi Murakawa, and Keiya Shirahama

    arXiv:2107.07398v2    1 - 19 2021.07

    Research paper (other science council materials etc.), Joint Work, Except for reviews

  • Evidence for 4D XY Quantum Criticality in 4He Confined in Nanoporous Media at Finite Temperatures

    Tomoyuki Tani, Yusuke Nago, Satoshi Murakawa, and Keiya Shirahama

    Journal of the Physical Society of Japan (Physical Society of Japan)  90 ( 3 ) 033601-1 - 033601-5 2021.02

    Research paper (scientific journal), Joint Work, Accepted,  ISSN  00319015

     View Summary

    4He confined in nanoporous media is a model Bose system that exhibits quantum phase transition (QPT) by varying pressure. We have precisely determined the critical exponent of the superfluid density of liquid 4He in porous Gelsil glasses with pore size of 3.0 nm using the Helmholtz resonator technique. The critical exponent ζ of the superfluid density was found to be 1.0 ± 0.1 for the pressure range 0.1 < P < 2.4 MPa. This value provides decisive evidence that the finite-temperature superfluid transition belongs to the four-dimensional (4D) XY universality class, in contrast to the classical 3D XY one in bulk liquid 4He, in which ζ = 0.67. The quantum critical behavior at a finite temperature is understood by strong phase fluctuations in local Bose-Einstein condensates above the superfluid transition temperature. 4He in nanoporous media is a unique example in which quantum criticality emerges not only at 0K but at finite temperatures.

  • 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

     View Summary

    © 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

     View Summary

    © 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.

display all >>

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

Presentations 【 Display / hide

  • 水素薄膜の低温における誘電率の異常挙動

    白濱圭也, 道川真丹, 伊藤愛菜, 谷智行, 永合祐輔

    日本物理学会第2021年秋季大会 (オンライン) , 2021.09, Oral Presentation(general)

  • 4D XY Quantum Criticality of Superfluid 4He confined in Gelsil Glass

    T. Tani, Y. Nago, S. Murakawa, and K. Shirahama

    2021 International Symposium on Quantum Fluids and Solids(QFS2021) (the Centre for Nano Science and Engineering (CeNSE) at the Indian Institute of Science (IISc), Bangalore, India) , 2021.08, Poster (general)

  • 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

    桑原啓佑, 鈴木貴博, 永合祐輔, 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)

  • 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

    鈴木貴博, 巻内崇彦, 永合祐輔, 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)

display all >>

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)

     View Summary


  • 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)

     View Summary


  • 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

     View Summary

    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

     View Summary

    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)

     View Summary

    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.

display all >>

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


     View Details

    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











display all >>

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

display all >>


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