Exciton-polarons in two-dimensional semiconductors and the Tavis-Cummings model

TL;DR

This paper uses an analogy to the Tavis-Cummings model to interpret exciton-polarons in 2D semiconductors as hybrid quasiparticles, offering new insights into their spectral properties and the nature of trions.

Contribution

It introduces a novel theoretical framework linking exciton-polarons to the Tavis-Cummings model, clarifying their composition as superpositions of excitons and trions.

Findings

Exciton-polarons are described as hybrid quasiparticles involving excitons and trions.

The analogy explains differences in absorption and emission spectra of 2D semiconductors.

The Chevy Ansatz effectively models dynamical screening in this context.

Abstract

The elementary optical excitations of a two-dimensional electron or hole system have been identified as exciton-Fermi-polarons. Nevertheless, the connection between the bound state of an exciton and an electron, termed trion, and exciton-polarons is subject of ongoing debate. Here, we use an analogy to the Tavis-Cummings model of quantum optics to show that an exciton-polaron can be understood as a hybrid quasiparticle -- a coherent superposition of a bare exciton in an unperturbed Fermi sea and a bright collective excitation of many trions. The analogy is valid to the extent that the Chevy Ansatz provides a good description of dynamical screening of excitons and provided the Fermi energy is much smaller than the trion binding energy. We anticipate our results to bring new insight that could help to explain the striking differences between absorption and emission spectra of two-dimensional semiconductors.