Spontaneous Chiral Symmetry Breaking in Bilayer Graphene

TL;DR

This paper reviews the theoretical predictions and experimental observations of spontaneous chiral symmetry breaking in bilayer graphene, highlighting the emergence of topological many-body ground states due to electron interactions.

Contribution

It synthesizes existing theories and recent experimental results on chiral symmetry breaking and topological states in bilayer graphene.

Findings

Theories predict spontaneous charge transfer between layers leading to energy gaps.

Recent experiments observe signatures consistent with chiral symmetry breaking.

Topological many-body ground states are identified in bilayer graphene.

Abstract

Bilayer graphene and its thicker cousins with Rhombohedral stacking have attracted considerable attention because of their susceptibility to a variety of broken chiral symmetry states. Due to large density-of-states and quantized Berry phases near their gapless band touching points, each spin-valley flavor spontaneously transfers charge between layers to yield opening of energy gaps in quasiparticle spectra and spreading of momentum-space Berry curvatures. In this article we review the development of theories that predicted such chiral symmetry breaking and classified the possible topological many-body ground states, and the observations in recent experiments that are in reasonable agreement with these theories.