Valley filtering by a line-defect in graphene: quantum interference and inversion of the filter effect

TL;DR

This paper investigates how a line-defect in graphene can act as a valley filter and demonstrates how external gate voltages can invert this filtering effect through quantum interference mechanisms.

Contribution

It introduces a detailed atomistic model with mode decomposition to understand valley filtering and its inversion via Fano resonance effects in graphene.

Findings

Valley filtering can be inverted by external gate voltages.

Quantum interference causes a Fano resonance that reduces conductance.

Gate voltage tuning enables control over valley transport.

Abstract

Valley filters are crucial to any device exploiting the valley degree of freedom. By using an atomistic model, we analyze the mechanism leading to the valley filtering produced by a line-defect in graphene and show how it can be inverted by external means. Thanks to a mode decomposition applied to a tight-binding model we can resolve the different transport channels in k-space while keeping a simple but accurate description of the band structure, both close and further away from the Dirac point. This allows the understanding of a destructive interference effect (Fano resonance or antiresonance) on the p-side of the Dirac point leading to a reduced conductance. We show that in the neighborhood of this feature the valley filtering can be reversed by changing the occupations with a gate voltage, the mechanism is explained in terms of a valley-dependent Fano resonance splitting. Our results open the door for an enhanced control of valley transport in graphene-based devices.