Crystallization of an exciton superfluid

TL;DR

This paper demonstrates that indirect exciton superfluids in semiconductor quantum wells can crystallize under compression, then melt back into superfluids, revealing complex quantum phase behavior driven by many-particle effects.

Contribution

It provides the first phase diagram of exciton states showing crystallization and melting, based on first-principles simulations, and predicts experimental conditions for observing these phenomena.

Findings

Exciton superfluid crystallizes upon compression.

Further compression induces quantum melting back to superfluid.

Phase diagram predicts experimental parameters for observing exciton crystallization.

Abstract

Indirect excitons -- pairs of electrons and holes spatially separated in semiconductor bilayers or quantum wells -- are known to undergo Bose-Einstein condensation and to form a quantum fluid. Here we show that this superfluid may crystallize upon compression. However, further compression results in quantum melting back to a superfluid. This unusual behavior is explained by the effective interaction potential between indirect excitons which strongly deviates from a dipole potential at small distances due to many-particle and quantum effects. Based on first principle path integral Monte Carlo simulations, we compute the complete phase diagram of this system and predict the relevant parameters necessary to experimentally observe exciton crystallization in semiconductor quantum wells.