Attractive and repulsive exciton-polariton interactions mediated by an electron gas

TL;DR

This paper investigates how an electron gas in a semiconductor microcavity mediates attractive and repulsive interactions between exciton-polaritons, with potential for enhanced non-linear optical applications.

Contribution

It introduces a microscopic many-body theory showing tunable, strong mediated interactions between polaritons via an electron gas, surpassing direct interactions.

Findings

Electron-hole excitations mediate attractive polariton interactions.

Trion-polariton interactions can be attractive or repulsive depending on the branch.

Mediated interactions can be over ten times stronger than direct polariton interactions.

Abstract

Realising strong photon-photon interactions in a solid-state setting is a major goal with far reaching potential for optoelectronic applications. Using Landau's quasiparticle framework combined with a microscopic many-body theory, we explore the interactions between exciton-polaritons and trions in a two-dimensional semiconductor injected with an electron gas inside a microcavity. We show that particle-hole excitations in the electron gas mediate an attractive interaction between the polaritons, whereas a trion-polariton interaction mediated by the exchange of an electron is either repulsive or attractive depending on the specific polariton branch. These mediated interactions are intrinsic to the quasiparticles and are also present in the absence of light. Importantly, they can be tuned to be more than an order of magnitude stronger than the direct polariton-polariton interaction in the absence of the electron gas, thereby providing a promising outlook for non-linear optical components. Finally, we compare our theoretical predictions with two recent experiments.