  (Ga,Mn)As is a paradigm diluted magnetic semiconductor which shows
ferromagnetism induced by doped hole carriers. With a few controversial models
emerged from numerous experimental and theoretical studies, the mechanism of
the ferromagnetism in (Ga,Mn)As still remains a puzzling enigma. In this
Letter, we use soft x-ray angle-resolved photoemission spectroscopy to
positively identify the ferromagnetic Mn 3d-derived impurity band in (Ga,Mn)As.
The band appears hybridized with the light-hole band of the host GaAs. These
findings conclude the picture of the valence band structure of (Ga,Mn)As
disputed for more than a decade. The non-dispersive character of the IB and its
location in vicinity of the valence-band maximum indicate that the Mn
3d-derived impurity band is formed as a split-off Mn-impurity state predicted
by the Anderson impurity model. Responsible for the ferromagnetism in (Ga,Mn)As
is the transport of hole carriers in the impurity band.
