# Observation of Large Unidirectional Rashba Magnetoresistance in Ge(111)

## TL;DR

This study reports a significant unidirectional magnetoresistance in Ge(111) surfaces, linked to spin textures and Rashba effects, with potential for semiconductor device applications.

## Contribution

First observation of large unidirectional Rashba magnetoresistance in Ge(111), highlighting the role of spin-split surface states and external magnetic fields.

## Key findings

- Magnetoresistance is linear in current density and magnetic field.
- At 15 K, the effect reaches 0.5% of zero field resistance.
- The effect diminishes with temperature and gate voltage changes.

## Abstract

Relating magnetotransport properties to specific spin textures at surfaces or interfaces is an intense field of research nowadays. Here, we investigate the variation of the electrical resistance of Ge(111) grown epitaxially on semi-insulating Si(111) under the application of an external magnetic field. We find a magnetoresistance term which is linear in current density j and magnetic field B, hence odd in j and B, corresponding to a unidirectional magnetoresistance. At 15 K, for I = 10 $\mu$A (or j = 0.33 A/m) and B = 1 T, it represents 0.5 % of the zero field resistance, a much higher value compared to previous reports on unidirectional magnetoresistance. We ascribe the origin of this magnetoresistance to the interplay between the externally applied magnetic field and the current-induced pseudo-magnetic field in the spin-splitted subsurface states of Ge(111). This unidirectional magnetoresistance is independent of the current direction with respect to the Ge crystal axes. It progressively vanishes, either using a negative gate voltage due to carrier activation into the bulk (without spin-splitted bands), or by increasing the temperature due to the Rashba energy splitting of the subsurface states lower than $\sim$58 k$_B$. The highly developed technologies on semiconductor platforms would allow the rapid optimization of devices based on this phenomenon.