  Our experimental and theoretical study of the non-crystalline and crystalline
components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As is aimed at
exploring the basic physical aspects of this relativistic transport effect. The
non-crystalline AMR reflects anisotropic lifetimes of the holes due to
polarized Mn impurities while the crystalline AMR is associated with valence
band warping. We find that the sign of the non-crystalline AMR is determined by
the form of spin-orbit coupling in the host band and by the relative strengths
of the non-magnetic and magnetic contributions to the impurity potential. We
develop experimental methods directly yielding the non-crystalline and
crystalline AMR components which are then independently analyzed. We report the
observation of an AMR dominated by a large uniaxial crystalline component and
show that AMR can be modified by local strain relaxation. We discuss generic
implications of our experimental and theoretical findings including predictions
for non-crystalline AMR sign reversals in dilute moment systems.
