  The detailed nature of electronic states mediating ferromagnetic coupling in
dilute magnetic semiconductors, specifically (Ga,Mn)As, has been an issue of
long debate. Two confronting models have been discussed emphasizing host band
vs. impurity band carriers. Using angle resolved photoemission we are for the
first time able to identify a highly dispersive Mn-induced energy band in
(Ga,Mn)As. Our results show that the electronic structure of the (Ga,Mn)As
system is significantly modified from that of GaAs throughout the valence band.
Close to the Fermi energy, the presence of Mn induces a strong mixing of the
bulk bands of GaAs, which results in the appearance of a highly dispersive band
in the gap region of GaAs. For Mn concentrations above 1% the band reaches the
Fermi level, and can thus host the delocalized holes needed for ferromagnetic
coupling. Overall, our data provide a firm evidence of delocalized carriers
belonging to the modified host valence band.
