Valley switch in a graphene superlattice due to pseudo-Andreev reflection

TL;DR

This paper demonstrates a topologically-originated valley switch in graphene superlattices, where electrons can be reflected into the opposite valley with high efficiency, advancing valleytronics applications.

Contribution

It reveals a novel valley switching mechanism via superlattice reflection, linked to topological properties and analogous to Andreev reflection in superconductors.

Findings

Valley switch occurs near normal incidence at the interface.

The process is topologically protected and robust over a broad parameter range.

Reflection can achieve near 100% valley inversion.

Abstract

Dirac electrons in graphene have a valley degree of freedom that is being explored as a carrier of information. In that context of "valleytronics" one seeks to coherently manipulate the valley index. Here we show that reflection from a superlattice potential can provide a valley switch: Electrons approaching a pristine-graphene--superlattice-graphene interface near normal incidence are reflected in the opposite valley. We identify the topological origin of this valley switch, by mapping the problem onto that of Andreev reflection from a topological superconductor, with the electron-hole degree of freedom playing the role of the valley index. The valley switch is ideal at a symmetry point of the superlattice potential, but remains close to 100% in a broad parameter range.