Fermi-edge exciton-polaritons in doped semiconductor microcavities with finite hole mass

TL;DR

This paper develops an analytical approach to study how finite hole mass affects Fermi-edge exciton-polaritons in doped semiconductor microcavities, revealing contrasting effects depending on the Fermi energy regime.

Contribution

It introduces a diagrammatic method to analyze finite hole mass effects, bridging the gap between low and high Fermi energy regimes in exciton-polariton spectra.

Findings

Finite hole mass enhances excitonic features when Fermi energy is low.

Finite hole mass suppresses excitonic features when Fermi energy is high.

Results agree qualitatively with recent experimental observations.

Abstract

The coupling between a 2D semiconductor quantum well and an optical cavity gives rise to combined light-matter excitations, the exciton-polaritons. These were usually measured when the conduction band is empty, making the single polariton physics a simple single-body problem. The situation is dramatically different in the presence of a finite conduction band population, where the creation or annihilation of a single exciton involves a many-body shakeup of the Fermi sea. Recent experiments in this regime revealed a strong modification of the exciton-polariton spectrum. Previous theoretical studies concerned with nonzero Fermi energy mostly relied on the approximation of an immobile valence band hole with infinite mass, which is appropriate for low-mobility samples only; for high-mobility samples, one needs to consider a mobile hole with large but finite mass. To bridge this gap we present an analytical diagrammatic approach and tackle a model with short-ranged (screened) electron-hole interaction, studying it in two complementary regimes. We find that the finite hole mass has opposite effects on the exciton-polariton spectra in the two regimes: In the first, where the Fermi energy is much smaller than the exciton binding energy, excitonic features are enhanced by the finite mass. In the second regime, where the Fermi energy is much larger than the exciton binding energy, finite mass effects cut off the excitonic features in the polariton spectra, in qualitative agreement with recent experiments.