Theory of weak localization in ferromagnetic (Ga,Mn)As

We study quantum interference corrections to the conductivity in (Ga,Mn)As ferromagnetic semiconductors using a model with disordered valence-band holes coupled to localized Mn moments through a p-d kinetic-exchange interaction. We find that at Mn concentrations above 1% quantum interference corrections lead to negative magnetoresistance, i.e., to weak localization (WL) rather than weak antilocalization (WAL). Our work highlights key qualitative differences between (Ga,Mn)As and previously studied toy-model systems and pinpoints the mechanism by which exchange splitting in the ferromagnetic state converts valence-band WAL into WL. We comment on recent experimental studies and theoretical analyses of low-temperature magnetoresistance in (Ga,Mn)As which have been variously interpreted as implying both WL and WAL and as requiring an impurity-band interpretation of transport in metallic (Ga,Mn)As.