Excitation dynamics in excitonic condensation phase

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K14644
• 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: Keio University
• Principal Investigator: Sugimoto Koudai 慶應義塾大学, 理工学部(矢上), 講師 (70756072)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 励起子相 / 強相関電子系 / 数値計算 / 有限温度 / 光誘起相転移 / 非平衡ダイナミクス

Outline of Final Research Achievements

The phase in which excitons spontaneously form in a semimetal or semiconductor and subsequently undergo Bose condensation is referred to as an excitonic phase. In recent years, some potential materials have been proposed, and the study of excitonic phases has revealed novel perspectives. In this research, I conducted both theoretical and numerical analyses of finite-temperature states and photo-induced nonequilibrium states in strongly correlated electron systems, with particular attention to the physical properties of excitonic phases.
For the finite-temperature calculations, we expanded the variational cluster approach to include finite temperatures and applied the cluster mean-field approximation to the excitonic phase. In the examination of nonequilibrium states, we proposed light-induced phase transitions within the attractive and repulsive Hubbard models, and elucidated the effect of excitons on higher-harmonic generations in the extended Hubbard model.

Free Research Field

物性物理学

Academic Significance and Societal Importance of the Research Achievements

本研究では、有限温度計算により励起子相や反強磁性相といった自発的対称性の破れを伴う強相関電子系物質への理解が深まった。有限サイズ効果の問題により変分クラスター法を励起子相へ適用するには至らなかったものの、今後改善すればこの分野の大きな進展が期待される。加えて、非平衡ダイナミクスの研究を進め、数値シミュレーションを用いて強相関電子系に特有の光誘起相転移現象や高次高調波発生スペクトルを提唱した。これらは実験と直結する成果であり、その学術的意義は大きなものであると考えられる。