Extremely imbalanced two-dimensional electron-hole-photon systems

TL;DR

This paper explores how extreme charge imbalance in two-dimensional electron-hole systems coupled to microcavity photons influences various electron-hole pairing states and their observable effects in the photon spectrum.

Contribution

It introduces a variational approach to analyze competing electron-hole pairing states in imbalanced 2D systems within microcavities, highlighting the effects of Coulomb interactions and photon coupling.

Findings

Fermi sea modifies exciton properties and dielectric constant.

Long-range Coulomb interactions promote finite-momentum pairing.

Strong photon coupling favors zero-momentum pairs.

Abstract

We investigate the phases of two-dimensional electron-hole systems strongly coupled to a microcavity photon field in the limit of extreme charge imbalance. Using variational wave functions, we examine the competition between different electron-hole paired states for the specific cases of semiconducting III-V single quantum wells, electron-hole bilayers, and transition metal dichalcogenide monolayers embedded in a planar microcavity. We show how the Fermi sea of excess charges modifies both the electron-hole bound state (exciton) properties and the dielectric constant of the cavity active medium, which in turn affects the photon component of the many-body polariton ground state. On the one hand, long-range Coulomb interactions and Pauli blocking of the Fermi sea promote electron-hole pairing with finite center-of-mass momentum, corresponding to an excitonic roton minimum. On the other hand, the strong coupling to the ultra-low-mass cavity photon mode favors zero-momentum pairs. We discuss the prospect of observing different types of electron-hole pairing in the photon spectrum.