Persistent Current States in Bilayer Graphene

TL;DR

This paper explores how electron-electron interactions in bilayer graphene at finite density induce Pomeranchuk instabilities, leading to valley polarization and nematic phases with distinct symmetry-breaking features.

Contribution

It demonstrates the emergence of valley polarization and nematic phases driven by non-local exchange interactions in bilayer graphene.

Findings

Valley polarization breaks time-reversal symmetry.

Nematic phase reduces rotational symmetry.

Optical absorption depends on light polarization in nematic phase.

Abstract

We argue that at finite carrier density and large displacement fields, bilayer graphene is prone to $\ell =0$ and $\ell = 1$ Pomeranchuk Fermi surface instabilities. The broken symmetries are driven by non-local exchange interactions which favor momentum space condensation. We find that electron-electron interactions lead first to spontaneous valley polarization, which breaks time-reversal invariance and is associated with spontaneous orbital magnetism, and then under some circumstances to a nematic phase with reduced rotational symmetry. When present, nematic order is signaled by reduced symmetry in the dependence of optical absorption on light polarization.