Leaky exciton condensates in transition metal dichalcogenide moir\'e bilayers

TL;DR

This paper demonstrates that dark exciton condensates in transition metal dichalcogenide moiré bilayers are 'leaky', allowing optical emission through many-body interactions, and explores their properties and implications for excitonic ordering.

Contribution

It reveals that dark exciton condensates are not fully dark but exhibit leaky emission due to many-body effects, and analyzes their properties in twisted TMD bilayers.

Findings

Leaky condensates dominate low-temperature photoluminescence.

Distinctive qualitative features of emission are identified.

Intervalley physics can induce symmetry-breaking excitonic order.

Abstract

We show that the "dark condensates" that arise when excitons form a Bose-Einstein condensate in a material with an indirect bandgap are not completely dark to optical emission. Rather, such states are "leaky condensates" in which optical emission is facilitated by many-body interactions. We analyze the properties of these leaky condensates in the context of twisted bilayers of transition metal dichalcogenides, which host strongly interacting excitons and an indirect bandgap. We show that this interaction-driven "leaky" emission dominates photoluminescence at low temperatures, with distinctive qualitative features. Finally, we propose that in these materials, unique intervalley physics can lead to crystal symmetry-breaking excitonic ordering, with implications for optical processes.