Fermi edge polaritons in a highly degenerate 2D electron gas: a diagrammatic theory

TL;DR

This paper develops a diagrammatic theoretical model to study Fermi edge polaritons in highly doped 2D semiconductor microcavities, revealing how doping affects polariton lifetimes and the existence of quasiparticles.

Contribution

It introduces a ladder diagram approximation to analyze the impact of high doping on polariton properties, including lifetime and quasiparticle formation.

Findings

Strong light-matter coupling persists at high doping levels.

Lower polariton remains qualitatively unchanged but gains a finite lifetime.

A narrow upper polariton quasiparticle can exist despite being in the electron-hole continuum.

Abstract

We present a theoretical study on polaritons in highly doped semiconductor microcavities. In particular, we focus on a cavity mode that is resonant with the absorption threshold (`Fermi edge'). In agreement with experimental results, the strong light-matter coupling is maintained under very high doping within our ladder diagram approximation. While the lower polariton is qualitatively unaltered, it acquires a finite lifetime due to relaxation of the valence band hole if the electron density exceeds a certain critical value. On the other hand the upper polariton has a finite lifetime for all densities, because it lies in the electron-hole continuum where no bound state exists. Our calculations show that a narrow upper polariton quasiparticle still exists as a result from the interplay between light-matter coupling and final state Coulomb interaction.