Study of Electronic Structures in Two-Dimensional Crystals and Their Stacked Materials Using Micro Angle-Resolved Photoemission Spectroscopy

Abstract

Two-dimensional (2D) crystals exhibit unique electronic structures depending on the number of layers, differing from their bulk counterparts. Recent advances allow the fabrication of van der Waals (vdW) heterostructures, stacked from 2D crystals with tunable configurations, such as twist angles and material combinations, opening a vast landscape of unexplored phenomena. However, determining atomic coordinates in these microscale samples, crucial for band calculations, remains challenging. To address this, we developed a sample preparation process compatible with complex vdW heterostructures for angle-resolved photoemission spectroscopy, enabling direct observation of their electronic structures. This revealed layer-number-dependent band structures and spin-splitting in few-layer WTe₂, demonstrating odd-even layer-number effects. Moreover, 180°-twisted stacking of monolayers of T-polytype transition metal dichalcogenides was shown to break spatial inversion symmetry, unlocking new electronic functionalities and broadening the potential for discovering unique properties in 2D materials.