Revealing the conduction band and pseudovector potential in 2D moir\'e semiconductors

TL;DR

This study uses advanced photoemission techniques to explore the electronic structure of moiré heterobilayers, revealing details about the conduction band, effective mass, and the influence of pseudovector potentials due to strain.

Contribution

It provides direct experimental evidence of the conduction band properties and moiré potential effects in 2D heterobilayers, highlighting the role of pseudovector potentials in band formation.

Findings

Conduction band edge at K-point with 1.58 eV gap

Small effective mass of 0.15 m_e observed

Moiré replicas influenced by pseudovector potential

Abstract

Stacking monolayer semiconductors results in moir\'e patterns that host many correlated and topological electronic phenomena, but measurements of the basic electronic structure underpinning these phenomena are scarce. Here, we investigate the properties of the conduction band in moir\'e heterobilayers using submicron angle-resolved photoemission spectroscopy with electrostatic gating, focusing on the example of WS2/WSe2. We find that at all twist angles the conduction band edge is the K-point valley of the WS2, with a band gap of 1.58 +- 0.03 eV. By resolving the conduction band dispersion, we observe an unexpectedly small effective mass of 0.15 +- 0.02 m_e. In addition, we observe replicas of the conduction band displaced by reciprocal lattice vectors of the moir\'e superlattice. We present arguments and evidence that the replicas are due to modification of the conduction band states by the moir\'e potential rather than to final-state diffraction. Interestingly, the replicas display an intensity pattern with reduced, 3-fold symmetry, which we show implicates the pseudo vector potential associated with in-plane strain in moir\'e band formation.