Dual Spin Filter Effect in a Zigzag Graphene Nanoribbon

TL;DR

This study demonstrates a dual spin filter effect in symmetric zigzag graphene nanoribbons under bias, where up- and down-spin electrons are unidirectionally filtered, driven by band structure and wave function symmetry.

Contribution

It reveals a novel dual spin filter mechanism in symmetric ZGNRs, distinct from conventional half-metallic devices, based on first-principles calculations and theoretical analysis.

Findings

Dual spin filter effect observed under finite bias.

Asymmetric ZGNRs do not show this effect.

Band structure and wave function symmetry are key factors.

Abstract

By first principle calculations, a dual spin filter effect under finite bias voltages is demonstrated in an antiferromagnetic junction of symmetric zigzag graphene nanoribbon (ZGNR). Unlike conventional spin filter devices using half metallic materials, the up- and down-spin electrons are unidirectionally filtered in the counter direction of the bias voltage, making the junction a dual spin filter. On the contrary, asymmetric ZGNRs do not exhibit such a spin filter effect. By analyzing Wannier functions and a tight-binding model, we clarify that an interplay between the spin polarized band structure of $\pi$ and $\pi^*$ states near the Fermi level and decoupling of the interband hopping of the two states, arising from the symmetry of the wave functions, plays a crucial role in the effect.