Elucidation and control of topological order in quantum spin liquids

• Project/Area Number: 21K13881
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: Kyoto University
• Principal Investigator: Suetsugu Shota 京都大学, 理学研究科, 助教 (00893710)
• Project Period (FY): 2021-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000); Fiscal Year 2022: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000); Fiscal Year 2021: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
• Keywords: 量子スピン液体 / トポロジー

Outline of Research at the Start

局在スピンが絶対零度においても秩序化・凍結せずに揺らいでいる状態を量子スピン液体と呼ぶ。その中でも量子スピン液体状態を基底状態として持つキタエフ模型は、局在スピンがマヨラナ粒子に分数化するため非可換エニオンなどのマヨラナ粒子によるトポロジカル励起を探索する格好の舞台となっている。
本研究ではキタエフ型量子スピン液体候補物質であるα-RuCl3において、磁気トルク・熱伝導度の磁場角度依存性を調べ、キタエフ模型のトポロジカル相を解明する。本研究を通じて、電子相関の効果で生じるトポロジーの研究を、トポロジカル相制御下におけるトポロジカル励起探索の段階へと進展させる。

Outline of Final Research Achievements

Quantum spin liquids, in which localized spins fluctuate without magnetic order or spin freezing even at absolute zero temperature, have attracted much attention because the localized spins fractionalized into different degrees of freedom, such as Majorana fermions. Although α-RuCl3 is known as a candidate material for the quantum spin liquid, it has been controversial whether the quantum spin liquid state is actually realized or not. In this project, we have demonstrated the existence of a first-order phase transition in a magnetic field by the specific heat and thermal conductivity experiments on α-RuCl3. Our results indicate the presence of the quantum spin liquid phase in α-RuCl3.

Academic Significance and Societal Importance of the Research Achievements

量子スピン液体状態で現れるマヨラナ粒子は環境ノイズに強いトポロジカル量子計算の実現に必要なため注目を集めている。本研究ではその候補物質であるα-RuCl3において確かに量子スピン液体状態が実現していることを示し、これまでの論争に決着をつけた。以上の研究成果により量子スピン液体状態の存在が確立されたため、今後はマヨラナ粒子を探索する研究がさらに加速することが期待される。

Research Products

• [Journal Article] Evidence for a Phase Transition in the Quantum Spin Liquid State of a Kitaev Candidate α-RuCl3 (2022)
  • Author(s): Suetsugu Shota、Ukai Yuzuki、Shimomura Masaki、Kamimura Masashi、Asaba Tomoya、Kasahara Yuichi、Kurita Nobuyuki、Tanaka Hidekazu、Shibauchi Takasada、Nasu Joji、Motome Yukitoshi、Matsuda Yuji
  • Journal Title: Journal of the Physical Society of Japan Volume: 91 Issue: 12 Pages: 124703-124703
  • DOI: 10.7566/jpsj.91.124703
  • Peer Reviewed / Open Access
• [Journal Article] Quantized and unquantized thermal Hall conductance of the Kitaev spin liquid candidate α-RuCl3 (2022)
  • Author(s): Kasahara Y.、Suetsugu S.、Asaba T.、Kasahara S.、Shibauchi T.、Kurita N.、Tanaka H.、Matsuda Y.
  • Journal Title: Physical Review B Volume: 106 Issue: 6
  • DOI: 10.1103/physrevb.106.l060410
  • Peer Reviewed / Open Access
• [Journal Article] Intrinsic suppression of the topological thermal Hall effect in an exactly solvable quantum magnet (2022)
  • Author(s): S. Suetsugu, T. Yokoi, K. Totsuka, T. Ono, I. Tanaka, S. Kasahara, Y. Kasahara, Z. Chengchao, H. Kageyama, and Y. Matsuda
  • Journal Title: Physical Review B Volume: 105 Issue: 2 Pages: 024415-024415
  • DOI: 10.1103/physrevb.105.024415
  • Peer Reviewed
• [Presentation] Fully gapped pairing states in spin-triplet superconductor UTe2 (2023)
  • Author(s): Shota Suetsugu, M. Shimomura, M. Kamimura, T. Asaba, H. Asaeda, Y. Kosuge, Y. Sekino, S. Ikemori, Y. Kasahara, Y. Kohsaka, M. Lee, Y. Yanase, H. Sakai, P. Opletal, Y. Tokiwa, Y. Haga, and Y. Matsuda
  • Organizer: APS March Meeting 2023
  • Int'l Joint Research
• [Presentation] Fully gapped pairing states in spin-triplet superconductor UTe2 (2022)
  • Author(s): Shota Suetsugu, M. Shimomura, M. Kamimura, T. Asaba, H. Asaeda, Y. Kosuge, Y. Sekino, S. Ikemori, Y. Kasahara, Y. Kohsaka, Y. Yanase, H. Sakai, P. Opletal, Y. Tokiwa, Y. Haga, and Y. Matsuda
  • Organizer: 非自明な電子状態で発現する超伝導現象の新しい潮流
• [Presentation] Field-induced first-order topological phase transition in a Kitaev spin liquid candidate α-RuCl3 (2022)
  • Author(s): S. Suetsugu, Y. Ukai, M. Shimomura, M. Kamimura, T. Asaba, Y. Kasahara, N. Kurita, H. Tanaka, T. Shibauchi, J. Nasu, Y. Motome, Y. Matsuda
  • Organizer: APS March meeting 2022
  • Int'l Joint Research