Polaritons in an electron gas -- quasiparticles and Landau effective interactions

TL;DR

This paper develops a microscopic framework to analyze polaron-polaritons in 2D semiconductors within microcavities, revealing their interactions, measurable spectral features, and attractive effective interactions that influence their energy shifts.

Contribution

It introduces a comprehensive microscopic model for polaron-polaritons, deriving parameters for Landau theory and applying the ladder approximation to explore their properties.

Findings

Polaron-polaritons can be characterized by microscopic parameters.

Their interactions can be measured via light transmission/reflection spectra.

Electron-hole excitations mediate attractive Landau effective interactions.

Abstract

Two-dimensional semiconductors inside optical microcavities have emerged as a versatile platform to explore new hybrid light-matter quantum states. The strong light-matter coupling leads to the formation of exciton-polaritons, which in turn interact with the surrounding electron gas to form quasiparticles called polaron-polaritons. Here, we develop a general microscopic framework to calculate the properties of these quasiparticles such as their energy and the interactions between them. From this, we give microscopic expressions for the parameters entering a Landau theory for the polaron-polaritons, which offers a simple yet powerful way to describe such interacting light-matter many-body systems. As an example of the application of our framework, we then use the ladder approximation to explore the properties of the polaron-polaritons. We furthermore show that they can be measured in a non-demolition way via the light transmission/reflection spectrum of the system. Finally, we demonstrate that the Landau effective interaction mediated by electron-hole excitation is attractive leading to red shifts of the polaron-polaritons. Our work provides a systematic framework to study exciton-polaritons in electronically doped two-dimensional materials such as novel van der Waals heterostructures.