Graphene Nanobubbles as Valley Filters and Beamsplitters

TL;DR

This paper proposes a novel method to achieve valley polarization in graphene using strain-induced pseudomagnetic fields from nanobubbles, enabling valley filtering and splitting without external magnetic fields.

Contribution

It introduces a strain-based approach for valleytronics in graphene, avoiding external magnetic fields and utilizing nanobubbles to manipulate valley-specific electron trajectories.

Findings

Nanobubbles induce pseudomagnetic fields that differentiate valley trajectories.

The method enables valley filtering and splitting in graphene.

Simulations show multiple device functionalities based on deformation fields.

Abstract

The low energy band structure of graphene has two inequivalent valleys at K and K' points of the Brillouin zone. The possibility to manipulate this valley degree of freedom defines the field of valleytronics, the valley analogue of spintronics. A key requirement for valleytronic devices is the ability to break the valley degeneracy by filtering and spatially splitting valleys to generate valley polarized currents. Here we suggest a way to obtain valley polarization using strain-induced inhomogeneous pseudomagnetic fields (PMF) which act differently on the two valleys. Notably, the suggested method does not involve external magnetic fields, or magnetic materials, as previous proposals. In our proposal the strain is due to experimentally feasible nanobubbles (but any local deformation would do): the associated PMFs lead to different real space trajectories for K and K' electrons, thus allowing the two valleys to be addressed individually. In this way, graphene nanobubbles can be exploited in both valley filtering and valley splitting devices, and our simulations reveal that a number of different functionalities are possible depending on the deformation field.