Evidence for a Superfluid-to-solid Transition of Bilayer Excitons

TL;DR

This paper reports the experimental observation of a superfluid to insulator transition in bilayer magneto-excitons, suggesting the existence of a quantum coherent excitonic solid phase driven by interactions.

Contribution

First experimental evidence of a superfluid-to-insulator transition in bilayer excitons indicating a possible excitonic solid phase without external lattice potential.

Findings

Observation of a superfluid-insulator transition in bilayer excitons

Insulating phase is an ordered state stabilized by dipole interactions

Insulator melts into superfluid with increasing temperature

Abstract

One of the most spectacular properties associated with Bose-Einstein condensation (BEC) is superfluidity in which the system exhibits zero viscosity and flows without dissipation. The superfluid phase has been observed in wide ranging Bosonic systems spanning naturally occurring quantum fluids, such as liquid helium, to engineered platforms such as bilayer excitons and cold atom systems. Theoretical works have proposed that interactions could drive the BEC ground state into another exotic phase that simultaneously exhibits properties of both a crystalline solid and a superfluid - termed a supersolid. Identifying a material system, however, that hosts the predicted BEC solid phase, driven purely by interactions and without imposing an external lattice potential, has remained elusive. Here we report observation of a superfluid to insulator transition in the layer-imbalanced regime of bilayer magneto-excitons. Mapping the transport behavior of the bilayer condensate as a function of density and temperature, suggests that the insulating phase is an ordered state of dilute excitons, stabilized by dipole interactions. The insulator melts into a recovered superfluid upon increasing the temperature, which could indicate that the low temperature solid is also a quantum coherent phase.