Zener tunneling isospin Hall effect in HgTe quantum wells and graphene multilayers

TL;DR

This paper investigates Zener tunneling in HgTe quantum wells and graphene multilayers, revealing an asymmetric transition probability that leads to a spin/valley Hall effect driven by Berry phase effects.

Contribution

It uncovers a novel Zener tunneling spin/valley Hall effect in these materials, linking it to Berry phase acquired during adiabatic reflection.

Findings

Asymmetric tunneling transition probability depending on momentum

Opposite asymmetry for spins in HgTe quantum wells

Opposite asymmetry for valleys in graphene multilayers

Abstract

A Zener diode is a paradigmatic device in semiconductor-based electronics that consists of a pn junction where an external electric field induces a switching behavior in the current-voltage characteristics. We study Zener tunneling in HgTe quantum wells and graphene multilayers. We find that the tunneling transition probability depends asymmetrically on the parallel momentum of the carriers to the barrier. In HgTe quantum wells the asymmetry is the opposite for each spin, whereas for graphene multilayers it is the opposite for each valley degree of freedom. In both cases, a spin/valley current flowing in the perpendicular direction to the applied field is produced. We relate the origin of this Zener tunneling spin/valley Hall effect to the Berry phase acquired by the carriers when they are adiabatically reflected from the gapped region.