Global phase diagram of charge neutral graphene in the quantum Hall regime for generic interactions

TL;DR

This paper maps the complete phase diagram of charge neutral graphene in a magnetic field, revealing various coexisting ordered phases under generic interactions, extending previous models beyond ultra short-range assumptions.

Contribution

It provides the full phase diagram of $ u=0$ graphene using the continuum limit and generic symmetry-allowed interactions, including coexisting orders and effects of a sublattice potential.

Findings

Multiple phases with coexisting orders identified

Presence of Kekulé bond order and charge density wave

Phase diagram extends beyond ultra short-range interaction models

Abstract

Monolayer graphene at charge neutrality in a quantizing magnetic field is a quantum Hall ferromagnet. Due to the spin and valley (near) degeneracies, there is a plethora of possible ground states. Previous theoretical work, based on a stringent ultra short-range assumption on the symmetry-allowed interactions, predicts a phase diagram with distinct regions of spin-polarized, canted antiferromagnetic, inter-valley coherent, and charge density wave order. While early experiments suggested that the system was in the canted antiferromagnetic phase at a perpendicular field, recent scanning tunneling studies universally find Kekul\'e bond order, and sometimes also charge density wave order. Recently, it was found that if one relaxes the stringent assumption mentioned above, a phase with coexisting canted antiferromagnetic and Kekul\'e order exists in the region of the phase diagram believed to correspond to real samples. In this work, starting from the continuum limit appropriate for experiments, we present the complete phase diagram of $\nu=0$ graphene in the Hartree-Fock approximation, using generic symmetry-allowed interactions, assuming translation invariant ground states up to an intervalley coherence. Allowing for a sublattice potential (valley Zeeman coupling), we find numerous phases with different types of coexisting order. We conclude with a discussion of the physical signatures of the various states.