Phase diagram for the $\nu=0$ quantum Hall state in monolayer graphene

TL;DR

This paper maps the phase diagram of the $ u=0$ quantum Hall state in monolayer graphene, revealing how electron interactions and Landau level mixing influence various ordered phases.

Contribution

It provides a systematic analysis of pseudospin anisotropies and Landau level effects, identifying four distinct phases and how interactions determine their stability.

Findings

Landau level mixing enhances anisotropy energies

Sign of anisotropy energies can change due to renormalization

Electron-phonon interactions favor Kekulé distortion

Abstract

The $\nu=0$ quantum Hall state in a defect-free graphene sample is studied within the framework of quantum Hall ferromagnetism. We perform a systematic analysis of the pseudospin anisotropies, which arise from the valley and sublattice asymmetric short-range electron-electron (e-e) and electron-phonon (e-ph) interactions. The phase diagram, obtained in the presence of generic pseudospin anisotropy and the Zeeman effect, consists of four phases characterized by the following orders: spin-polarized ferromagnetic, canted antiferromagnetic, charge density wave, and Kekul\'{e} distortion. We take into account the Landau level mixing effects and show that they result in the key renormalizations of parameters. First, the absolute values of the anisotropy energies become greatly enhanced and can significantly exceed the Zeeman energy. Second, the signs of the anisotropy energies due to e-e interactions can change upon renormalization. A crucial consequence of the latter is that the short-range e-e interactions alone could favor any state on the phase diagram, depending on the details of interactions at the lattice scale. On the other hand, the leading e-ph interactions always favor the Kekul\'{e} distortion order. The possibility of inducing phase transitions by tilting the magnetic field is discussed.