Furukawa, Shunsuke



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


Assistant Professor/Senior Assistant Professor

E-mail Address

E-mail address

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Career 【 Display / hide

  • 2007.04

    RIKEN, Condensed Matter Theory Laboratory, Special Postdoctoral Researcher

  • 2009.09

    University of Toronto, Department of Physics, Postdoctoral Fellow

  • 2011.07

    University of Tokyo, Department of Physics, Postdoctoral Researcher

  • 2012.08

    University of Tokyo, Department of Physics, Assistant Professor

  • 2019.04

    Keio University, Department of Physics, Assistant Professor

Academic Background 【 Display / hide

  • 1999.04

    Tokyo Institute of Technology, School of Science, Department of Physics

    University, Skipped grade(s)

  • 2002.04

    Tokyo Institute of Technology, Graduate School of Science, Department of Physics

    Graduate School, Completed, Master's course

  • 2004.04

    Tokyo Institute of Technology, Graduate School of Science, Department of Physics

    Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide

  • 博士(理学), Tokyo Institute of Technology, Coursework, 2007.03

    Characterization of Exotic Orders in Quantum Spin Systems


Research Areas 【 Display / hide

  • Mathematical physics/Fundamental condensed matter physics

  • Atomic/Molecular/Quantum electronics

Research Keywords 【 Display / hide

  • topological states of matter

  • ultracold atomic systems

  • magnetism

Research Themes 【 Display / hide

  • Quantum critical phenomena in non-Hermitian quantum many-body systems, 


  • Theory of frustrated magnetism of volborthite based on a coupled-trimer model, 


  • Quantum Hall physics of ultracold atomic systems in synthetic gauge fields, 


  • Elementary excitations and a spin model of multiferroic BiFeO3


  • Orders and multiferroics in spin-1/2 frustrated ferromagnetic chains, 


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Papers 【 Display / hide

  • Continuous Phase Transition without Gap Closing in Non-Hermitian Quantum Many-Body Systems

    Matsumoto Norifumi, Kawabata Kohei, Ashida Yuto, Furukawa Shunsuke, Ueda Masahito

    Physical Review Letters (Physical Review Letters)  125 ( 26 )  2020.12

    ISSN  0031-9007

     View Summary

    © 2020 American Physical Society. Contrary to the conventional wisdom in Hermitian systems, a continuous quantum phase transition between gapped phases is shown to occur without closing the energy gap Δ in non-Hermitian quantum many-body systems. Here, the relevant length scale ζ≃vLR/Δ diverges because of the breakdown of the Lieb-Robinson bound on the velocity (i.e., unboundedness of vLR) rather than vanishing of the energy gap Δ. The susceptibility to a change in the system parameter exhibits a singularity due to nonorthogonality of eigenstates. As an illustrative example, we present an exactly solvable model by generalizing Kitaev's toric-code model to a non-Hermitian regime.

  • Probing XY phase transitions in a Josephson junction array with tunable frustration

    Cosmic R., Kawabata K., Ashida Y., Ikegami H., Furukawa S., Patil P., Taylor J. M., Nakamura Y.

    PHYSICAL REVIEW B (Physical Review B)  102 ( 9 )  2020.09

    ISSN  2469-9950

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    © 2020 American Physical Society. The seminal theoretical works of Berezinskii, Kosterlitz, and Thouless presented a paradigm for phase transitions in condensed matter that are driven by topological excitations. These transitions have been extensively studied in the context of two-dimensional XY models-coupled compasses- A nd have generated interest in the context of quantum simulation. Here, we use a circuit quantum-electrodynamics architecture to study the critical behavior of engineered XY models through their dynamical response. In particular, we examine not only the unfrustrated case but also the fully frustrated case which leads to enhanced degeneracy associated with the spin rotational [U(1)] and discrete chiral (Z2) symmetries. The nature of the transition in the frustrated case has posed a challenge for theoretical studies while direct experimental probes remain elusive. Here we identify the transition temperatures for both the unfrustrated and fully frustrated XY models by probing a Josephson junction array close to equilibrium using weak microwave excitations and measuring the temperature dependence of the effective damping obtained from the complex reflection coefficient. We argue that our probing technique is primarily sensitive to the dynamics of the U(1) part.

  • Effects of Dzyaloshinskii-Moriya Interactions in Volborthite: Magnetic Orders and Thermal Hall Effect

    Furukawa Shunsuke, Momoi Tsutomu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN (Physical Society of Japan)  89 ( 3 ) 034711 - 034711 2020.03

    Research paper (scientific journal), Joint Work, Accepted,  ISSN  0031-9015

     View Summary

    © 2020 The Author(s) Volborthite offers an interesting example of a highly frustrated quantum magnet in which ferromagnetic and antiferromagnetic interactions compete on anisotropic kagome lattices. A recent density functional theory calculation has provided a magnetic model based on coupled trimers, which is consistent with a broad 13-magnetization plateau observed experimentally. Here we study the effects of Dzyaloshinskii-Moriya (DM) interactions in volborthite. We derive an effective model in which pseudospin-12 moments emerging on trimers form a network of an anisotropic triangular lattice. Using the effective model, we show that for a magnetic field perpendicular to the kagome layer, magnon excitations from the 13-plateau feel a Berry curvature due to the DM interactions, giving rise to a thermal Hall effect. Our magnon Bose gas theory can explain qualitative features of the magnetization and the thermal Hall conductivity measured experimentally. A further quantitative comparison with experiment poses constraints on the coupling constants in the effective model, promoting a quasi-one-dimensional picture. Based on this picture, we analyze low-temperature magnetic phase diagrams using effective field theory, and point out their crucial dependence on the field direction.

  • Magnetoelastic couplings in the deformed kagome quantum spin lattice of volborthite

    A. Ikeda, S. Furukawa, O. Janson, Y. H. Matsuda, S. Takeyama, T. Yajima, Z. Hiroi, H. Ishikawa

    Physical Review B (Physical Review B)  99 ( 14 )  2019.04

    Research paper (scientific journal), Joint Work, Accepted,  ISSN  2469-9969

     View Summary

    © 2019 American Physical Society. Microscopic spin interactions on a deformed kagome lattice of volborthite are investigated through magnetoelastic couplings. A negative longitudinal magnetostriction ΔL/L<0 in the b axis is observed, which depends on the magnetization M with a peculiar relation of ΔL/L�M1.3. Based on the exchange striction model, it is argued that the negative magnetostriction originates from a pantographlike lattice change of the Cu-O-Cu chain in the b axis, and that the peculiar dependence arises from the local spin correlation. This idea is supported by DFT+U calculations simulating the lattice change and a finite-size calculation of the spin correlation, indicating that the recently proposed coupled-trimer model is a plausible one.

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Reviews, Commentaries, etc. 【 Display / hide

  • Entanglement entropy and conformal field theory

    S. Furukawa, J. Shiraishi

    BUTSURI 69   541 - 546 2014

    Introduction and explanation (scientific journal), Joint Work

Presentations 【 Display / hide

  • Spontaneous symmetry breaking and symmetry-protected topological phases in a spin-1/2 XXZ ladder with a four-spin interaction

    T. Ogino, R. Kaneko, S. Morita, S. Furukawa, N. Kawashima

    日本物理学会第76回年次大会 (オンライン開催) , 2021.03, Oral Presentation(general)

  • 人工ゲージ場中の二成分Bose-Einstein凝縮体における渦格子の集団励起と結合定数の繰り込み

    Takumi Yoshino, Shunsuke Furukawa, Masahito Ueda

    日本物理学会第76回年次大会 (オンライン開催) , 2021.03, Oral Presentation(general)

  • 二成分Bose-Einstein凝縮体における成分間エンタングルメント・エントロピー

    古川俊輔, 吉野匠, 上田正仁

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

  • スピンラダー系におけるNeel-VBS連続相転移の数値的検証2

    荻野卓啓, 金子隆威, 森田悟史, 川島直輝, 古川俊輔

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

  • ボルボサイトにおけるDzyaloshinskii-Moriya相互作用の効果II

    古川俊輔, 桃井勉

    日本物理学会第75回年次大会 (名古屋大学東山キャンパス) , 2020.03, Poster (general)

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

  • Theoretical study of many-body effects in Bose-Einstein condensates in synthetic gauge fields


    Keio Gijuku, Academic Development Funds, Shunsuke Furukawa, Research grant, Principal Investigator

  • Symmetry-enriched topological phases: theoretical foundation and proposal for realization


    MEXT,JSPS, Grant-in-Aid for Scientific Research, 古川 俊輔, Grant-in-Aid for Scientific Research (C), Principal Investigator

  • Phase frustration in Bose-Einstein condensates in optical lattices


    Matsuo Foundation, Shunsuke Furukawa, Research grant, Principal Investigator

  • Exploration of topological orders in strongly correlated ultracold atomic systems and development of their fundamental theory


    The University of Tokyo, FURUKAWA SHUNSUKE, Grant-in-Aid for Young Scientists (B)

     View Summary

    Topologically ordered states exhibit a number of intriguing properties such as quantized responses and quasiparticles obeying fractional statistics. In this study, we have theoretically explored novel topologically ordered states that can be realized in highly controlled ultracold atomic systems, and investigated their physical properties. In particular, we have determined detailed ground-state phase diagrams of two-component Bose gases in synthetic gauge fields, and revealed (i) the appearance of a bosonic integer quantum Hall state with unusual edge states and (ii) a nontrivial role of time-reversal symmetry in the interaction effect. We have also shown that Bose-Einstein condensate in optical lattices can host an excitation band with nontrivial topology, and that edge states originating from it can be observed by exploiting a macroscopic quantum interference.

Awards 【 Display / hide

  • The 2nd High Magnetic Field Forum Frontier Incentive Award

    Shunsuke Furukawa, 2020.12, The High Magnetic Field Forum of Japan, Theoretical studies on quantum magnets with competing ferromagnetic and antiferromagnetic interactions

    Type of Award: Awards of National Conference, Council and Symposium

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  • The 7th Young Scientist Award of the Physical Society of Japan

    Shunsuke Furukawa, 2013.03, Physical Society of Japan, Entanglement entropy in quantum many-body systems

    Type of Award: Awards of National Conference, Council and Symposium

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Courses Taught 【 Display / hide











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