  We have investigated the nonreciprocal electrical transport, that is a
nonlinear resistance effect depending on the current direction, in multiferroic
Rashba semiconductor (Ge,Mn)Te. Due to coexistence of ferromagnetic and
ferroelectric orders, (Ge,Mn)Te provides a unique platform for exploring the
nonreciprocal electrical transport in a bulk form. (Ge,Mn)Te thin films shows a
large nonreciprocal resistance compared to GeTe, the nonmagnetic counterpart
with the same crystal structure. The magnetic-field-angle dependence of the
nonreciprocal resistance is maximized when magnetic field is orthogonal to both
current and electric polarization, in accord with the symmetry argument. From
the analysis of temperature and magnetic field dependence, we deduce that
inelastic scatterings of electrons mediated by magnons dominantly contribute to
the observed nonreciprocal response. Furthermore, the nonreciprocal resistance
is significantly enhanced by lowering hole density. The Fermi level dependence
is attributed to the deformation of the Rashba band in which the spin-momentum
locked single Fermi surface appears by exchange field from the in-plane
magnetization. The present study provides a key insight to the mechanisms of
novel transport phenomena caused by the interplay of ferroelectric and
ferromagnetic orders in a semiconductor.
