# Rashba spin-orbit coupling enhanced magnetoresistance in junctions with one ferromagnet

## TL;DR

This paper explores how Rashba spin-orbit coupling can significantly enhance magnetoresistance in junctions with a single ferromagnet, especially when superconductivity and spin-dependent Andreev reflection are involved, revealing complex nonmonotonic behaviors.

## Contribution

It demonstrates the role of Rashba SOC in inducing large, nonmonotonic magnetoresistance effects through spin-dependent Andreev reflection in ferromagnet-superconductor junctions.

## Key findings

- Rashba SOC can cause nonmonotonic magnetoresistance sign changes.
- Enhanced magnetoresistance observed in ferromagnet-superconductor junctions.
- Proximity-induced equal-spin-triplet superconductivity evidenced by magnetoresistance trends.

## Abstract

We explain how Rashba spin-orbit coupling (SOC) in a two-dimensional electron gas (2DEG), or in a conventional $s$-wave superconductor, can lead to a large magnetoresistance even with one ferromagnet. However, such enhanced magnetoresistance is not generic and can be nonmonotonic and change its sign with Rashba SOC. For an in-plane rotation of magnetization, it is typically negligibly small for a 2DEG and depends on the perfect transmission which emerges from a spin-parity-time symmetry of the scattering states, while this symmetry is generally absent from the Hamiltonian of the system. The key difference from considering the normal-state magnetoresistance is the presence of the spin-dependent Andreev reflection at superconducting interfaces. In the fabricated junctions of quasi-2D van der Waals ferromagnets with conventional $s$-wave superconductors (Fe$_{0.29}$TaS$_2$/NbN) we find another example of enhanced magnetoresistance where the presence of Rashba SOC reduces the effective interfacial strength and is responsible for an equal-spin Andreev reflection. The observed nonmonotonic trend in the out-of-plane magnetoresistance with the interfacial barrier is an evidence for the proximity-induced equal-spin-triplet superconductivity.