Probing the collective excitations of excitonic insulators in an optical cavity

TL;DR

This paper investigates how light-matter coupling in optical cavities influences collective excitations in excitonic insulators, revealing unique interactions that alter photon dispersion and are absent in other phases.

Contribution

It introduces a model showing the coupling between collective phase modes and cavity photons, highlighting unique effects in excitonic insulators not seen in trivial or topological phases.

Findings

Collective excitations significantly affect photon dispersion.

Avoiding band crossing occurs in excitonic insulators.

Effects are absent in trivial, topological, and phonon-mediated phases.

Abstract

The light--matter interaction in optical cavities offers a promising ground to create hybrid states and manipulate material properties. In this work, we examine the effect of light-matter coupling in the excitonic insulator phase using a quasi one-dimensional lattice model with two opposite parity orbitals at each site. We show that the model allows for a coupling between the collective phase mode and cavity photons. Our findings reveal that the collective mode of the excitonic state significantly impacts the dispersion of the cavity mode, giving rise to an avoiding band crossing in the photon dispersion. This phenomenon is absent in trivial and topological insulator phases and also in phonon-mediated excitonic insulators, underscoring the unique characteristics of collective excitations in excitonic insulators. Our results demonstrate the significant impact of light-matter interaction on photon propagation in the presence of excitonic collective excitations.