Excitons in a reconstructed moiré potential in twisted WSe2/WSe2 homobilayers

Abstract

Moiré superlattices in twisted van der Waals (vdW) materials have recently emerged as a promising platform for engineering electronic and optical properties. A major obstacle to fully understanding these systems and harnessing their potential is the limited ability to correlate direct imaging of the moiré structure with optical and electronic properties. Here, we develop a secondary electron microscope technique to directly image stacking domains in fully functional vdW heterostructure devices. After demonstrating imaging of AB/BA and ABA/ABC domains in multi-layer graphene, we employ this technique to investigate reconstructed moiré patterns in twisted bilayer WSe2/WSe2 and directly correlate increasing moiré periodicity with the emergence of two distinct exciton species in photoluminescence measurements. These states can be tuned individually through electrostatic gating and feature different valley coherence properties. Our observations can be understood as resulting from the formation of an array of two intralayer exciton species residing in alternating locations in the superlattice, and open up new avenues for realizing tunable exciton arrays in twisted vdW heterostructures, with applications in quantum optoelectronics and explorations of novel many body systems.