Temperature effects in excitonic condensation driven by the lattice distortion

TL;DR

This paper investigates how lattice distortions influence excitonic condensation in a 2D semimetal, revealing a temperature-dependent transition to an excitonic insulator with BCS-like characteristics.

Contribution

It introduces a self-consistent Hartree-Fock framework to analyze the interplay between lattice distortion and excitonic condensation, highlighting a temperature-driven phase transition.

Findings

Semimetal-insulator transition occurs at low temperature with strong electron-lattice coupling.

Excitonic condensate is accompanied by finite lattice distortion, favoring a BCS-like pairing.

Both the condensate and lattice distortion vanish at higher temperatures.

Abstract

The stability of the excitonic condensation at low temperature driven by a coupling of electrons to vibrational degrees of freedom in semimetal two-dimensional electronic system is discussed. In the framework of the unrestricted Hartree-Fock approximation, we derive a set of equations to determine both the excitonic condensate order parameter and lattice displacement self-consistently. By lowering temperature we find out a semimetal-insulator transition in the system if the coupling is large enough. The insulating state typifies an excitonic condensation accompanied by a finite lattice distortion. Increasing temperature, both excitonic condensate order parameter and the lattice distortion decrease and then disappear in the same manner. Microscopic analysis in momentum space strongly specifies that the excitonic condensate driven by the lattice distortion favours the BCS type.