Topological electronic structure of few-layer and bulk van der Waals materials probed by angle-resolved photoemission

Abstract

Van der Waals materials can be exfoliated down to atomically thin crystals, offering potential to explore physics in lower dimensionality. In this thesis, I investigated their topological electronic structure with ARPES. I studied mono-, bi- and few-layer Td-WTe2. The small size of exfoliated crystals and their air-sensitivity pose new challenges for standard ARPES setups, successfully overcome in the present study. The measurements showed the topological band gap in the monolayer, a strong Rashba splitting in the bilayer, and thickness-dependent quantum-well states up to thicknesses above 15 layers. I describe conventional measurements on the recently grown Pt2HgSe3. ARPES measurements on the bulk crystal were motivated by the prediction of a record-high topological band gap in the monolayer. This implies a weak topological insulator in the bulk with surface states only on lateral surfaces. However, ARPES measurements showed surface states on the top surface, revealing a richer topological picture.