Trimer superfluidity of antiparallel dipolar excitons in a bilayer heterostructure

TL;DR

This paper investigates a bilayer system of antiparallel dipolar excitons, revealing a novel trimer superfluid phase formed by three-exciton bound states, and explores the phase transitions influenced by temperature and density.

Contribution

It introduces the concept of trimer superfluidity in dipolar excitons and maps the phase diagram, including quantum and thermal phase transitions, using quantum Monte Carlo simulations.

Findings

Existence of a trimer superfluid phase at low temperatures and densities.

Quantum phase transition from trimer superfluid to two-superfluid phase with increasing density.

Thermal transitions involve intermediate states such as a trimer superfluid or single excitonic condensate.

Abstract

We study the phase diagram of a bilayer of antiparallel dipolar excitons with a 1:2 density ratio between the layers, as a function of temperature and density. Using quantum Monte Carlo simulations, we show that such a system supports the formation of trimers, namely, three-exciton bound states consisting of a single dipole in one layer and two dipoles in the second layer. At sufficiently low temperatures and densities, these trimers condense into a trimer superfluid phase. Increasing the excitonic density induces a quantum phase transition into a phase in which condensates of independent dipoles exist in both layers, in parallel to the trimers. We also study the thermal transitions out of these phases, and find that while the normal state is reached directly from the trimer superfluid, the thermal disordering of the two-superfluid phase involves an intermediate state which is either a trimer superfluid or a single excitonic condensate in the denser layer. A potential experimental realization using transition metal dichalcogenide heterostructures is discussed.