Pure spin current and perfect valley filter by designed separation of the chiral states in two-dimensional honeycomb lattices

TL;DR

This paper presents a method to generate pure spin currents and perfect valley filtering in two-dimensional honeycomb lattices by spatially separating chiral edge states using boundary potentials, with robustness against scattering.

Contribution

It introduces a novel approach to control edge states in quantum anomalous Hall insulators for spin and valley filtering through boundary potential engineering.

Findings

Spatial separation of spin-polarized edge states achieved.

Valley filter immunity to various scatterers demonstrated.

Boundary potential controls size effect oscillations.

Abstract

We propose a realization of pure spin currents and perfect valley filter based on a quantum anomalous Hall insulator, around which edge states with up-spin and down-spin circulate. By applying staggered sublattice potential on the strips along the edges of sample, the edge states with down spin can be pushed into the inner boundaries of the strips while the other edge states with up spin remain on the outer boundaries, resulting in spatially separated chiral states with perfect spin polarization. Moreover, a valley filter, which is immune to short-range and smooth long-range scatterers, can be engineered by additionally applying boundary potentials on the outmost lattices of the sample. We also find that the boundary potential can be used to control the size effect induced oscillation of the inner chiral states. The connection of the boundary potential to size effect is revealed.