Valley filtering and electronic optics using polycrystalline graphene

TL;DR

This paper theoretically investigates how polycrystalline graphene can be used to manipulate valley-polarized currents and exhibit optical-like behaviors, such as negative refraction, through strain-induced effects and grain boundary engineering.

Contribution

It introduces a theoretical framework showing how strain and grain boundaries in polycrystalline graphene enable valley filtering and electron optics functionalities.

Findings

Strain causes strong valley polarization in transmission.

Grain boundaries act as media for electron wave modulation.

Negative refraction indices can be achieved in polycrystalline graphene.

Abstract

In this Letter, both the manipulation of valley-polarized currents and the optical-like behaviors of Dirac fermions are theoretically explored in polycrystalline graphene. When strain is applied, the misorientation between two graphene domains separated by a grain boundary can result in a mismatch of their electronic structures. Such a discrepancy manifests itself in a strong breaking of the inversion symmetry, leading to perfect valley polarization in a wide range of transmission directions. In addition, these graphene domains act as different media for electron waves, offering the possibility to modulate and obtain negative refraction indexes.