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

磁性半導体(Ga,Mn)Asにおける強磁性を引き起こす不純物バンドの解明

小林 正起*; 宗田 伊理也*; 竹田 幸治   ; 原田 慈久*; 藤森 淳*; Krempask, J.*; Schmitt, T.*; 大矢 忍*; 田中 雅明*; 尾嶋 正治*; Strocov, V. N.*

Kobayashi, Masaki*; Muneta, Iriya*; Takeda, Yukiharu; Harada, Yoshihisa*; Fujimori, Atsushi*; Krempask, J.*; Schmitt, T.*; Oya, Shinobu*; Tanaka, Masaaki*; Oshima, Masaharu*; Strocov, V. N.*

(Ga,Mn)As is a paradigm of a diluted magnetic semiconductor which shows ferromagnetism induced by doped hole carriers. With a few controversial models emerging from numerous experimental and theoretical studies, the mechanism of the ferromagnetism in (Ga,Mn)As still remains a puzzling enigma. In this article, we use soft X-ray angle-resolved photoemission spectroscopy to positively identify the ferromagnetic Mn 3d-derived impurity band (IB) in (Ga,Mn)As. The band appears dispersionless and 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 nondispersive character of the IB and its location in vicinity of the valence-band maximum indicate that the Mn 3d-derived IB is formed as a split-off Mn-impurity state predicted by the Anderson.