Pseudospin Order in Monolayer, Bilayer, and Double-Layer Graphene

TL;DR

This paper explores how the unique phase relationships in graphene's wavefunctions enable various broken symmetry states, such as antiferromagnetic and exciton condensates, across different graphene structures.

Contribution

It provides a theoretical explanation for the emergence of broken symmetry states in monolayer, bilayer, and double-layer graphene based on their wavefunction phase differences.

Findings

Identification of conditions for broken symmetry states in graphene

Comparison of antiferromagnetic and exciton condensate states

Insight into momentum space analogs of real-space order

Abstract

Graphene is a gapless semiconductor in which conduction and valence band wavefunctions differ only in the phase difference between their projections onto the two sublattices of the material's two-dimensional honeycomb crystal structure. We explain why this circumstance creates openings for broken symmetry states, including antiferromagnetic states in monolayer and bilayer graphene and exciton condensates in double-layer graphene, that are momentum space analogs of the real-space order common in systems with strong local interactions. We discuss some similarities among, and some differences between, these three broken symmetry states.