Absence of edge states at armchair edges in inhomogeneously strained graphene under a pseudomagnetic field

TL;DR

This paper demonstrates that in inhomogeneously strained graphene, valley-polarized edge states only appear at zigzag edges and not at armchair edges due to valley mixing, contrasting with real magnetic field effects.

Contribution

It reveals the absence of edge states at armchair edges in strained graphene under pseudomagnetic fields, highlighting the role of valley mixing and edge type.

Findings

Valley-polarized edge states exist only at zigzag edges.

Armchair edges do not support edge states due to valley mixing.

Proposed interface state can transport electrons in a valley-polarized manner.

Abstract

Nonuniform strain in graphene can induce a pseudo-magnetic field (PMF) preserving time-reversal symmetry, generating pseudo-Landau levels under zero real magnetic field (MF). The different natures between PMF and real MF lead to the counterpropagating valley-polarized edge states under the PMF and unidirectionally chiral edge states under the real MF. In this work, we find, due to the valley mixing on the armchair edges, the quantum valley Hall edge states only exist at the zigzag edges but not at armchair edges in a uniaxial strained graphene, very different from the case that chiral quantum Hall edge states exist at all edges in pristine graphene under a real MF. We theoretically demonstrate it through the wave function distributions, multi-terminal transport measurements and the electron local occupations, respectively. The interface state in a p-n junction under PMF is further proposed to transport electrons between the conductive zigzag boundaries, which could be used as a valley-polarized single pole double throw switch.