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.Comment: 16 pages, 10 figures; submitted to Phys. Rev.
