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 moire superlattices. IX transport in transition-metal dichalcogenide heterostructures was intensively studied and diffusive IX transport with 1/e decay distances up to similar to 4 mu m was realized. Here, in a MoSe2/WSe2 heterostructure, we present the IX long-range transport with 1/e decay distances reaching and exceeding 100 mu m. The IX long-range transport vanishes at temperatures above similar to 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 moire superlattices.