Transport and localization of indirect excitons in a van der Waals heterostructure

Long lifetimes of spatially indirect excitons (IXs), also known as interlayer excitons, allow implementing both quantum exciton systems and long-range exciton transport. The van der Waals heterostructures composed of atomically thin layers of transition-metal dichalcogenides offer the opportunity to explore IXs in moiré superlattices. IX transport in transition-metal dichalcogenide heterostructures was intensively studied and diffusive IX transport with 1/e decay distances up to ~4 μm was realized. Here, in a MoSe2/WSe2 heterostructure, we present the IX long-range transport with 1/e decay distances reaching and exceeding 100 μm. The IX long-range transport vanishes at temperatures above ~10 K. With increasing IX density, IX localization followed by IX long-range transport and IX re-entrant localization are observed. The non-monotonic dependence of IX transport on density is in qualitative agreement with the Bose–Hubbard theory prediction for superfluid and insulating phases in periodic potentials of moiré superlattices. Spatial distribution of the photoluminescence of interlayer excitons in van der Waals heterostructures comprising MoSe2 and WSe2 monolayers and encapsulated in rather thick hexagonal boron nitride is investigated, revealing interlayer exciton long-range transport with 1/e decay distances reaching and exceeding 100 μm.