Dynamical Screening and Ferroelectric-type Excitonic Instability in Bilayer Graphene

TL;DR

This paper develops a controlled theoretical framework for understanding how electron interactions cause excitonic instability and energy gap opening in bilayer graphene, highlighting the role of dynamical screening and ultraviolet cutoff effects.

Contribution

It introduces a new theory accounting for dynamical screening and ultraviolet cutoff, explaining the power-law scaling of the energy gap in bilayer graphene.

Findings

Energy gap scales as a power law of interaction strength

Instability occurs even for weak interactions in bilayer graphene

Dynamical screening significantly influences excitonic instability

Abstract

Electron interactions in undoped bilayer graphene lead to instability of the gapless state, `which-layer' symmetry breaking, and energy gap opening at the Dirac point. In contrast to single layer graphene, the bilayer system exhibits instability even for arbitrarily weak interaction. A controlled theory of this instability for realistic dynamically screened Coulomb interactions is developed, with full acount of dynamically generated ultraviolet cutoff. This leads to an energy gap that scales as a power law of the interaction strength, making the excitonic instability readily observable.