Excitonic instability in two-dimensional degenerate semimetals

TL;DR

This paper investigates the potential for excitonic pairing in two-dimensional semimetals with Dirac-like electrons, revealing a critical Coulomb interaction strength and a transition akin to the Kosterlitz-Thouless phase change.

Contribution

It provides a numerical analysis of excitonic instability in layered semimetals, identifying a critical Coulomb coupling and characterizing the transition as Kosterlitz-Thouless-like.

Findings

Existence of a critical Coulomb coupling for excitonic pairing

Identification of a Kosterlitz-Thouless-like transition

Potential for excitonic insulator phase in layered semimetals

Abstract

We study the possibility of excitonic pairing in layered degenerate semimetals such as graphite, where the electron density of states almost vanishes at the Fermi level and, therefore, the Coulomb interactions remain essentially unscreened. By focusing on the Dirac-like low-energy electron excitations and numerically solving a non-linear gap equation for the order parameter, we obtain a critical value of the Coulomb coupling and establish the Kosterlitz-Thouless-like nature of a putative semimetal-to-excitonic insulator transition.