Spectral properties of excitons in the bilayer graphene

TL;DR

This paper investigates the spectral properties of excitons in bilayer graphene, revealing how interlayer Coulomb interactions induce a semimetal-semiconductor transition and exploring excitonic condensate states across coupling regimes.

Contribution

It introduces a detailed analysis of excitonic effects in bilayer graphene using a generalized Hubbard model, highlighting the transition mechanisms and spectral features.

Findings

Interlayer Coulomb interaction causes a semimetal-semiconductor transition.

Hybridization gap appears above a critical interaction strength.

Weak coupling exhibits BCS-like pairing; strong coupling shows excitonic condensates.

Abstract

In this paper, we consider the spectral properties of the bilayer graphene with the local excitonic pairing interaction between the electrons and holes. We consider the generalized Hubbard model, which includes both intralayer and interlayer Coulomb interaction parameters. The solution of the excitonic gap parameter is used to calculate the electronic band structure, single-particle spectral functions, the hybridization gap, and the excitonic coherence length in the bilayer graphene. We show that the local interlayer Coulomb interaction is responsible for the semimetal-semiconductor transition in the double layer system, and we calculate the hybridization gap in the band structure above the critical interaction value. The formation of the excitonic band gap is reported as the threshold process and the momentum distribution functions have been calculated numerically. We show that in the weak coupling limit the system is governed by the Bardeen-Cooper-Schrieffer (BCS)-like pairing state. Contrary, in the strong coupling limit the excitonic condensate states appear in the semiconducting phase, by forming the Dirac's pockets in the reciprocal space.