Excitons in Atomically Thin Two-Dimensional Semiconductors and Moiré Structures

量子物理学・ナノサイエンス第413回セミナー

概要

Two-dimensional van der Waals materials exhibit novel photoexcited states, intriguing field-driven and time-dependent phenomena, and exotic ground states. Here, we present some recent theoretical advances in their understanding and predictions. Our studies reveal a rich diversity of excitons in transition metal dichalcogenide (TMD) moiré superlattices, including previously unforeseen intralayer charge-transfer moiré excitons. We have also discovered a self-driven exciton-Floquet effect in the time-resolved, angle-resolved photoemission spectroscopy of 2D materials, where exciton-induced satellite features and band renormalization emerge, analogous to the optical Floquet effect driven by photons. We further show that strong excitonic physics in 2D semiconductors can greatly enhance their nonlinear optical responses, such as shift currents and second- or higher-order harmonic generation. This has led to a remarkable phenomenon – the formation of light-induced shift current vortex crystals in TMD moiré systems. Finally, we predict that in certain intrinsic TMD 2D materials, spontaneously formed excitons condense into an unconventional excitonic insulator phase, characterized by emergent k-space spin textures and other telltale spectroscopic signatures.

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• 量子物理学・ナノサイエンス第413回セミナー

【共催】
• 東京科学大学 物質・情報卓越教育課程 ／ 物質・情報卓越コース
• 東京科学大学 理学院 物理学系
• 文部科学省科学研究費助成事業 学術変革領域研究(A)「２.５次元物質科学」