  The structure inversion asymmetry at surfaces and interfaces give rise to the
Rashba spin-orbit interaction (SOI), that breaks the spin degeneracy of surface
or interface states. Hence, when an electric current runs through a surface or
interface, this Rashba effect generates an effective magnetic field acting on
the electron spin. This provides an additional tool to manipulate the spin
state in materials such as Si and Ge that, in their bulk form, possess
inversion symmetry (or lack structural inersion asymmetry). The existence of
Rashba states could be demonstrated by photoemission spectroscopy at the
interface between different metals and Ge(111) and by spin-charge conversion
experiments at the Fe/Ge(111) interface even though made of two light elements.
In this work, we identify the fingerprint of the Rashba states at the
Fe/Ge(111) interface by magnetotransport measurements in the form of a large
unidirectional magnetoresistance of up to 0.1 \%. From its temperature
dependence, we find that the Rashba energy splitting is larger than in pure
Ge(111) subsurface states.
