Spin Seebeck effect of quantum spin liquid states

2019 Fiscal Year Final Research Report

• Project/Area Number: 18K18730
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 13:Condensed matter physics and related fields
• Research Institution: Osaka University (2019); The University of Tokyo (2018)
• Principal Investigator: Shimozawa Masaaki 大阪大学, 基礎工学研究科, 准教授 (40736162)
• Project Period (FY): 2018-06-29 – 2020-03-31
• Keywords: 量子スピン液体 / 量子常誘電

Outline of Final Research Achievements

To investigate the quantum spin liquid (QSL) states of κ-H3(Cat-EDT-TTF)2, we studied their effect of element substitution and spin Seebeck effect. We first performed the thermal conductivity and magnetic torque measurements for three types of κ-H3(Cat-X)2: X = EDT-d4-TTF, EDSe-TTF, EDT-ST. As a result, we have found that the gapless QSLs of κ-H3(Cat-EDT-TTF)2 are robust against the full substitution of X site that significantly affects both spin-1/2 triangular structures and hydrogen bonds. Considering the results of our dielectric permittivity measurements, we can conclude that in κ-H3(Cat-EDT-TTF)2, quantum proton fluctuations are an important factor for stabilizing the QSLs. Next, we tried to observe the spin Seebeck effect of κ-H3(Cat-EDT-TTF)2; however, we failed because the evaporation of platinum and tangsten with strong spin-orbit coupling on the clean surface of κ-H3(Cat-EDT-TTF)2 is difficult (this is future work).

Free Research Field

低温物性

Academic Significance and Societal Importance of the Research Achievements

量子スピン液体と量子常誘電状態が同時に実現しているκ-H3(Cat-EDT-TTF)2系の研究を行なった。この試料では、「スピン自由度」と「プロトン自由度」が同時に揺らぎ続けている量子スピン液体であり、従来のものとは一線を画する。本研究において元素置換効果を調べたところ、このような多自由度量子スピン液体は、通常のものに比べて外的要因に対して安定度が増すことが分かった。この結果は、長年問題であった量子スピン液体の安定化メカニズムを理解する上で、大きな手がかりになると考えられる。