BCS-BEC crossover of polaritonic condensates in mass-imbalanced semimetal/semiconductor microcavities

TL;DR

This paper investigates how mass imbalance and Coulomb interactions influence the phase structures and BCS-BEC crossover of polaritonic condensates in semiconductor and semimetal microcavities, using a two-band electron-hole model.

Contribution

It provides a unified theoretical framework analyzing the effects of mass imbalance and Coulomb interaction on polaritonic condensates and their crossover behavior.

Findings

In semiconductors, low-density BEC-like excitonic polaritons dominate with increasing density transitioning to BCS-like pairing.

In semimetals, BCS-type condensates prevail, with BEC coherence appearing under strong Coulomb interaction and large mass imbalance.

Luminescence spectra reveal clear signatures of the BCS-BEC crossover phenomena.

Abstract

The impacts of the mass imbalance and Coulomb interaction on the complex phase structures of the polaritonic condensates and their Bardeen-Cooper-Schrieffer (BCS)--Bose-Einstein condensation (BEC) crossover in semiconductor and semimetal microcavities are investigated. In the framework of the unrestricted Hartree-Fock approximation, a two-band electron-hole model involving photon mode is analyzed by treating Coulomb attraction and light-matter coupling on equal footing. The single-particle spectral functions and the luminescence properties are then examined. In the semiconducting regime, a positive band gap stabilizes tightly bound excitons and yields predominantly BEC-type excitoniclike polaritonic condensates at low density, while increasing excitation density and reducing mass imbalance drives a continuous crossover toward BCS-type pairing with intermediate and photoniclike polaritonic character. In contrast, the semimetallic regime favors itinerant electron-hole pairing, with BCS-type condensates dominating and BEC excitoniclike coherence emerging only at sufficiently strong Coulomb interaction and large mass imbalance situations. The evolution of luminescence spectra provides clear spectroscopic signatures of these crossover phenomena, offering a unified framework for understanding and controlling polaritonic condensates in microcavity systems.