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 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.
Institute of Physics (IOP), 2017.