Nonreciprocal transverse currents in Rashba metal junctions under out-of-plane Zeeman fields

TL;DR

This paper reveals a nonreciprocal transverse charge current in Rashba metal junctions under out-of-plane Zeeman fields, driven by symmetry breaking and evanescent modes, without needing in-plane magnetic fields.

Contribution

It uncovers a novel nonreciprocal transverse conductivity mechanism in Rashba systems induced by out-of-plane Zeeman fields at junctions, distinct from homogeneous systems.

Findings

Transverse conductivity depends on bias direction and peaks near the Zeeman energy.

Evanescent modes carry spin polarization that induces transverse current.

Bound states at the junction enhance conductivity when near the transport window.

Abstract

We study charge transport across a junction between a normal metal and a Rashba metal in the presence of a Zeeman field applied to the spin--orbit coupled region. While an out-of-plane Zeeman field does not generate a transverse response in a homogeneous Rashba system, we show that such a junction exhibits a finite transverse conductivity that is inherently nonreciprocal, i.e., it depends on the direction of the applied bias. We demonstrate that this effect originates from the breaking of the $k_y \to -k_y$ symmetry of the Hamiltonian in the presence of the Zeeman field, which prevents cancellation of transverse current contributions from opposite transverse momenta. We further show that evanescent modes in the spin--orbit coupled region play a crucial role by carrying a finite spin polarization that gives rise to a transverse current localized near the junction. The transverse conductivity exhibits a peak at an energy scale set by the Zeeman field, displays distinct behavior for opposite bias directions, and shows spatial dependence governed by the nature of the contributing modes. We also identify bound states at the junction for attractive barrier strengths, which enhance conductivity when their energies lie near the transport window. Our results reveal a mechanism for nonreciprocal transverse charge transport in Rashba systems without requiring in-plane magnetic fields or ferromagnetic contacts, and should be experimentally accessible in semiconductor heterostructures.