Exciton-polariton condensate in the van der Waals magnet CrSBr

TL;DR

This paper reports the observation of exciton-polariton Bose-Einstein condensation in the magnetic van der Waals material CrSBr, revealing magnetic control over quantum light-matter interactions and non-linear optical properties.

Contribution

It demonstrates for the first time the formation of a coherent exciton-polariton condensate in a magnetic van der Waals material, with magnetic order influencing the condensate's non-linearity.

Findings

Observation of exciton-polariton Bose-Einstein condensation in CrSBr.

Magnetic order affects the condensate's non-linearity, switching between attractive and repulsive interactions.

Coherence confirmed through quantum correlation measurements.

Abstract

Van der Waals magnets are an emergent material class of paramount interest for fundamental studies in coupling light with matter excitations, which are uniquely linked to their underlying magnetic properties. Among these materials, the semiconducting magnet CrSBr is possibly a first playground where we can study simultaneously the interaction of photons, magnons, and excitons at the quantum level. Here we demonstrate a coherent macroscopic quantum phase, the bosonic condensation of exciton-polaritons, emerging in a CrSBr flake embedded in a fully tunable cryogenic open optical cavity. The Bose condensate is characterized by a highly non-linear threshold-like behavior, and coherence manifests distinctly via its first and second order quantum correlations. We find that the condensate's non-linearity is highly susceptible to the magnetic order in CrSBr. Specially, it can encounter a sign change from attractive to repulsive interactions when the intrinsic antiferromagnetic order transforms to the forced ferromagnetic order. Our findings open a route towards magnetically controllable quantum fluids of light, and optomagnonic devices where spin magnetism is coupled to on-chip Bose-Einstein condensates.