Thermal and mass-asymmetry effects on static density susceptibility of electron-hole bilayer

Abstract

We have studied theoretically the effect of temperature and electron-hole mass-asymmetry on the phase diagram of an electron-hole bilayer (EHBL) system. To this endeavor, the static wave vector dependent density susceptibility is calculated over a wide range of system parameters (viz., particle number density rs, inter-layer spacing d and reduced temperature τ) by using the dynamical self-consistent mean-field theory of Singwi et al., suitably generalized to include the inter-layer interactions and thermal effects. The susceptibility contains vital information on spatial distribution of charges; in particular, the occurrence of a structural phase transition (if any) may manifest in it as a divergence at a wave vector representing the period of charge density. Our study shows that the EHBL may become unstable against a finite-T coupled Wigner crystal (WC) state below a critical density in the close proximity of electron and hole layers. As an interesting result, it is found that while thermal effects tend to oppose the localization of carriers, the attractive e-h correlations boosted by the e-h mass-asymmetry favor it. As a direct consequence of this, the critical density for the onset of phase transition to the WC state in the finite-T mass-asymmetric EHBL for τ = 0.125 approximately approaches the result of the mass-symmetric EHBL at T = 0K. To the best of our knowledge, this is the first theoretical prediction on finite-T EHBL. It should be interesting to study this prediction through quantum Monte Carlo simulations and/or experiments.