Tunable large Berry dipole in strained twisted bilayer graphene

TL;DR

This paper predicts that strain in twisted bilayer graphene induces a large, tunable Berry dipole that results in significant non-linear Hall effects, with potential for experimental observation and control.

Contribution

It introduces a theoretical framework showing how strain-induced Berry curvature in TBG creates a giant, tunable Berry dipole leading to observable non-linear Hall responses.

Findings

Berry dipole of order 10 nm or larger predicted in strained TBG

Non-linear Hall effect dominates linear valley current at accessible fields

Berry dipole tunable by strain, electron filling, gap, and temperature

Abstract

Recent experiments have measured local uniaxial strain fields in twisted bilayer graphene (TBG). Our calculations found that the finite Berry curvature generated by breaking the sublattice symmetry and the band proximity between narrow bands in these TBG induces a giant Berry dipole of order 10\,nm or larger. The large Berry dipole leads to transverse topological non-linear charge currents which dominates over the linear bulk valley current at experimentally accessible crossover in-plane electric field of $\sim 0.1 {\rm mV} / \mu \rm{m}$. This anomalous Hall effect, due to Berry dipole, is strongly tunable by the strain parameters, electron fillings, gap size, and temperature.