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Unveiling the impurity band inducing ferromagnetism in magnetic semiconductor (Ga,Mn)As

(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.