Unidirectional magnetoresistance in a bulk Rashba ferromagnet

The Rashba effect is the spin band splitting due to broken inversion symmetry through spin-orbit coupling, typically observed at surfaces and interfaces. Recently, some noncentrosymmetryic crystals have been found to have the bulk Rashba bands that are larger than surface/interface ones. Nonreciprocal transport of quantum particles such as electron, spin and phonon is known to occur by further breaking time reversal symmetry in such a material without inversion symmetry. In particular, the interplay with magnetism in spin-polarized bands may enhance the nonreciprocal charge transport. In this study, we investigated the unidirectional magnetoresistance in thin films of Ge_1-xMn_xTe, which is a bulk ferromagnetic Rashba semiconductor. The magnitude of nonreciprocal transport shows a strong dependence on carrier density, which suggests that the scattering process on Fermi surface is essential for the nonreciprocal transport in the system.