Theoretical Research of Topological Phenomena in Strongly Correlated Electronic Systems with High Degrees of Freedom

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05540
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Niigata University
• Principal Investigator: Takimoto Tetsuya 新潟大学, 自然科学系, 教授 (80397794)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 物性理論 / 強相関電子系 / トポロジー / 群論

Outline of Final Research Achievements

In order to construct a theoretical model with large degrees of freedom, we consider first all electron-hole pairs in a regular tetrahedron, where an s-orbital is considered at each corner-site of the regular tetrahedron. Then, these electron-hole pair operators are classified into irreducible representations of the tetrahedral group Td, which corresponds to the crystal coordinate system. Among 64 types of electron-hole operators totally, there are 12 types of spin configuration operators, including the All-In-All-Out spin configuration operator (SPO) belonging to A2 representation and SPO belonging to E representation. Summing up electron-hole operators with respect to the unit cell, the order parameter belonging to the representation is obtained to describe the corresponding phase transition. The purpose of the study is to search the topological transition in the ordered state with the order parameter. We also generalize our theory to the system with orbital degree of freedom.

Free Research Field

数物科学系

Academic Significance and Societal Importance of the Research Achievements

All-In-All-Outスピン秩序相における集団励起についての研究はクラスター多極子からの新たな解釈を与えることができたと考えている。２つ目のテーマについては、パイロクロア化合物という実際の物質と比較する際には結晶軸と局所的座標軸の関係を明らかにしたことにより，対象とする現象によらずこの系のミニマム模型を構築できたことは学術的に意義があったと考えている。