Theory of unconventional quantum Hall effect in strained graphene

TL;DR

This paper investigates how strain-induced pseudo-magnetic fields in graphene lead to an unconventional quantum Hall effect with oscillating conductivity and stabilized correlated states, combining theoretical and numerical approaches.

Contribution

It introduces a novel theoretical framework for understanding the quantum Hall effect in strained graphene with pseudo-magnetic fields, revealing new quantization sequences and correlated phases.

Findings

Unconventional quantized Hall conductivity oscillates between 0 and ±2 e^2/h.

Strain produces two sets of Landau levels with opposite chiralities.

Electron-electron interactions stabilize various correlated ground states.

Abstract

We show through both theoretical arguments and numerical calculations that graphene discerns an unconventional sequence of quantized Hall conductivity, when subject to both magnetic fields (B) and strain. The latter produces time-reversal symmetric pseudo/axial magnetic fields (b). The single-electron spectrum is composed of two interpenetrating sets of Landau levels (LLs), located at $\pm \sqrt{2 n |b \pm B|}$, $n=0, 1, 2, \cdots$. For $b>B$, these two sets of LLs have opposite \emph{chiralities}, resulting in {\em oscillating} Hall conductivity between 0 and $\mp 2 e^2/h$ in electron and hole doped system, respectively, as the chemical potential is tuned in the vicinity of the neutrality point. The electron-electron interactions stabilize various correlated ground states, e.g., spin-polarized, quantum spin-Hall insulators at and near the neutrality point, and possibly the anomalous Hall insulating phase at incommensurate filling $\sim B$. Such broken-symmetry ground states have similarities as well as significant differences from their counterparts in the absence of strain. For realistic strength of magnetic fields and interactions, we present scaling of the interaction-induced gap for various Hall states within the zeroth Landau level.