title: Impurity band conduction in a high temperature ferromagnetic semiconductor.
abstract: The band structure of a prototypical dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied across the phase diagram via infrared and optical spectroscopy. We prove that the Fermi energy (EF) resides in a Mn-induced impurity band (IB). Specifically the changes in the frequency dependent optical conductivity [sigma1(omega)] with carrier density are only consistent with EF lying in an IB. Furthermore, the large effective mass (m*) of the carriers inferred from our analysis of sigma1(omega) supports this conclusion. Our findings demonstrate that the metal to insulator transition in this DMS is qualitatively different from other III-V semiconductors doped with nonmagnetic impurities. We also provide insights into the anomalous transport properties of Ga1-xMnxAs.
authors.affiliation: Department of Physics, University of California, San Diego, California 92093-0319, USA. kburch@lanl.gov
authors.forename: K S
authors.initials: KS
authors.lastname: Burch
authors.forename: D B
authors.initials: DB
authors.lastname: Shrekenhamer
authors.forename: E J
authors.initials: EJ
authors.lastname: Singley
authors.forename: J
authors.initials: J
authors.lastname: Stephens
authors.forename: B L
authors.initials: BL
authors.lastname: Sheu
authors.forename: R K
authors.initials: RK
authors.lastname: Kawakami
authors.forename: P
authors.initials: P
authors.lastname: Schiffer
authors.forename: N
authors.initials: N
authors.lastname: Samarth
authors.forename: D D
authors.initials: DD
authors.lastname: Awschalom
authors.forename: D N
authors.initials: DN
authors.lastname: Basov