Layer Coherent Phase in Double Layer graphene at $\nu^{}_1=\nu^{}_2=0$

TL;DR

This paper investigates a novel layer coherent phase in double layer graphene at zero filling factors, revealing symmetry-breaking ground states and analyzing their properties and excitations.

Contribution

It introduces the existence of a layer coherent phase in double layer graphene at zero filling, extending understanding beyond monolayer graphene phases.

Findings

Layer coherent phase breaks layer U(1) symmetry.

Small magnetization appears at non-zero Zeeman coupling.

Bulk gapless modes are discussed via Goldstone theorem.

Abstract

In the recent advancement in graphene heterostructures, it is possible to create a double layer tunnel decoupled graphene system that has a strong interlayer electronic interaction. In this work, we restrict the parameters in the low energy effective Hamiltonian using simple symmetry arguments. Then, we study the ground state of this system in the Hartree-Fock approximation at $\nu^{}_1=\nu^{}_2=0$. In addition to the phases found in monolayer graphene, we found an existence of layer coherent phase which breaks the layer $U(1)$ symmetry. At non-zero Zeeman coupling strength ($E^{}_z$), this layer coherent state has a small magnetization, that vanishes when $E^{}_z$ tends to zero. We discuss the bulk gapless modes using the Goldstone theorem. We also comment on the edge structure for the layer coherent phase.