Study of exotic quantum states emergent from strong spin-orbit coupling on the basis of exactly solvable models

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K17747
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics II
• Research Institution: Yokohama National University (2018-2019); Tokyo Institute of Technology (2016-2017)
• Principal Investigator: Nasu Joji 横浜国立大学, 大学院工学研究院, 准教授 (40610639)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 強相関電子系 / スピン軌道相互作用

Outline of Final Research Achievements

We studied strongly correlated electron systems with strong spin-orbit coupling to clarify exotic quantum phenomena emergent in these systems. It is generally difficult to take account of electron correlations, spin-orbit coupling, and anisotropy intrinsic in the orbital degree of freedom, on an equal footing. To overcome this difficulty, we started from the strong coupling limit and systematic calculations were performed. As the results, we obtained the following outcomes.
1) We consider the Kugel-Khomskii model describing the spin and orbital degrees of freedom and analyze the stability of ordered states in the presence of the spin-orbit coupling.
2) We discussed the possibility of a superconducting state with spontaneously orbital selection. In addition, we clarified the phase diagram including symmetry-broken states. We also discussed the validity of the results by introducing the effective model in the strong coupling limit.

Free Research Field

物性理論

Academic Significance and Societal Importance of the Research Achievements

本研究課題では、強相関電子系における軌道自由度の果たす役割を明らかにするため、強相関極限を起点として、蜂の巣格子上の多軌道模型における量子スピン液体や3軌道ハバード模型における超伝導状態などの性質を明らかにした。有限温度における静的・動的性質に対して包括的かつ詳細な解析を行った。量子スピン液体や多軌道ハバード模型における超伝導は量子多体効果が顕著であり、解析することが困難であることが多いが、ここでは強相関極限の局在電子系の計算を平行して行うことで、その妥当性も議論していることに学術的な意義があると考える。