A Non-Hermitian Moir\'{e} Valley Filter

TL;DR

This paper proposes a graphene bilayer valley filter utilizing a non-Hermitian topological effect driven by a moiré pattern and heterostrain, achieving high valley polarization with robustness to imperfections.

Contribution

It introduces a novel non-Hermitian topological approach to valley filtering in graphene bilayers, enabling high polarization and tunability with relaxed fabrication constraints.

Findings

Nearly 100% valley polarization achievable

High tolerance to disorder and defects

Electrical tunability of the valley filter

Abstract

A valley filter capable of generating a valley-polarized current is a crucial element in valleytronics, yet its implementation remains challenging. Here, we propose a valley filter made of a graphene bilayer which exhibits a 1D moir\'{e} pattern in the overlapping region of the two layers controlled by heterostrain. In the presence of a lattice modulation between layers, electrons propagating in one layer can have valley-dependent dissipation due to valley asymmetric interlayer coupling, thus giving rise to a valley-polarized current. Such a process can be described by an effective non-Hermitian theory, in which the valley filter is driven by a valley-resolved non-Hermitian skin effect. Nearly 100\% valley-polarization can be achieved within a wide parameter range and the functionality of the valley filter is electrically tunable. The non-Hermitian topological scenario of the valley filter ensures high tolerance against imperfections such as disorder and edge defects. Our work opens a new route for efficient and robust valley filters while significantly relaxing the stringent implementation requirements.