Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer

TL;DR

This study investigates how strain and curvature influence the local electronic properties and band structures of twisted graphene bilayers, revealing potential for high-temperature quantum valley Hall effects.

Contribution

It demonstrates that strain and out-of-plane distortions induce pseudo-Landau levels and valley polarization, advancing understanding of strain effects in twisted bilayer graphene.

Findings

Decreased energy difference of van Hove singularities with strain

Formation of pseudo-Landau levels mimicking magnetic quantization

Valley polarization with a significant energy gap

Abstract

Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature. The strain and curvature strongly affect the local band structures of the twisted graphene bilayer; the energy difference of the two low-energy van Hove singularities decreases with increasing the lattice deformations and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle. The joint effect of strain and out-of-plane distortion in the graphene wrinkle also results in a valley polarization with a significant gap, i.e., the eight-fold degenerate Landau level at the charge neutrality point is splitted into two four-fold degenerate quartets polarized on each layer. These results suggest that strained graphene bilayer could be an ideal platform to realize the high-temperature zero-field quantum valley Hall effect.