Self-consistent screening enhances stability of the nonequilibrium excitonic insulator phase

TL;DR

This paper introduces a self-consistent screening method to predict the stability of the nonequilibrium excitonic insulator phase, showing it remains stable at high densities due to a vanishing dielectric function.

Contribution

The study develops a Hartree plus Screened Exchange scheme to accurately determine the critical density for phase transition in NEQ-EI systems.

Findings

NEQ-EI phase stable up to ~10^{12}cm^{-2} in MoS2 monolayers.

Self-consistent dielectric function vanishes at long wavelengths.

Method predicts transition point to free electron-hole plasma.

Abstract

The nonequilibrium excitonic insulator (NEQ-EI) is an excited state of matter characterized by a finite density of coherent excitons and a time-dependent macroscopic polarization. The stability of this exciton superfluid as the density grows is jeopardized by the increased screening efficiency of the looser excitons. In this work we put forward a Hartree plus Screened Exchange HSEX scheme to predict the critical density at which the transition toward a free electron-hole plasma occurs. The dielectric function is calculated self-consistently using the NEQ-EI polarization and found to vanish in the long-wavelength limit. This property makes the exciton superfluid stable up to relatively high densities. Numerical results for the MoS$_{2}$ monolayers indicate that the NEQ-EI phase survives up to densities of the order of $10^{12}\mathrm{cm}^{-2}$.