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

TL;DR

This study demonstrates long-range transport of indirect excitons in MoSe2/WSe2 heterostructures, with transport distances exceeding 100 micrometers, and explores their localization and phase behavior in moiré superlattices.

Contribution

It reports the observation of long-range exciton transport exceeding 100 micrometers and reentrant localization in TMD heterostructures, aligning with Bose-Hubbard theoretical predictions.

Findings

IX transport exceeds 100 μm at resonance

Transport vanishes at high temperatures

Reentrant localization observed with increasing IX density

Abstract

Long lifetimes of spatially indirect excitons (IXs), also known as interlayer excitons, allow implementing both quantum exciton systems and long-range exciton transport. Van der Waals heterostructures (HS) composed of atomically thin layers of transition-metal dichalcogenides (TMD) offer the opportunity to explore IXs in moir\'e superlattices. The moir\'e IXs in TMD HS form the materials platform for exploring the Bose-Hubbard physics and superfluid and insulating phases in periodic potentials. IX transport in TMD HS was intensively studied and diffusive IX transport with $1/e$ decay distances $d_{1/e}$ up to $\sim 3$ $\mu$m was realized. In this work, we present in MoSe$_2$/WSe$_2$ HS the IX long-range transport with $d_{1/e}$ exceeding 100 $\mu$m and diverging at the optical excitation resonant to spatially direct excitons. The IX long-range transport vanishes at high temperatures. With increasing IX density, IX localization, then IX long-range transport, and then IX reentrant localization is observed. The results are in qualitative agreement with the Bose-Hubbard theory of bosons in periodic potentials predicting superfluid at $N \sim 1/2$ and insulating at $N \sim 0$ and $N \sim 1$ phases for the number of bosons per site of the periodic potential $N$.