Phys. Rev. Lett. 97, 087208 (2006) [4 pages]

Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor

Abstract

References

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K. S. Burch^1,*, D. B. Shrekenhamer¹, E. J. Singley^1,†, J. Stephens², B. L. Sheu³, R. K. Kawakami^2,‡, P. Schiffer³, N. Samarth³, D. D. Awschalom², and D. N. Basov¹
¹Department of Physics, University of California, San Diego, California 92093-0319, USA
²Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA
³Department of Physics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

Received 31 March 2006; published 23 August 2006

The band structure of a prototypical dilute magnetic semiconductor (DMS), Ga_1-xMn_xAs, is studied across the phase diagram via infrared and optical spectroscopy. We prove that the Fermi energy (E_F) resides in a Mn-induced impurity band (IB). Specifically the changes in the frequency dependent optical conductivity [σ₁(ω)] with carrier density are only consistent with E_F lying in an IB. Furthermore, the large effective mass (m^*) of the carriers inferred from our analysis of σ₁(ω) 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 Ga_1-xMn_xAs.

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.97.087208

DOI:

10.1103/PhysRevLett.97.087208

PACS:

75.50.Pp, 71.30.+h, 78.30.−j

^*Permanent address: Los Alamos National Laboratory, MS G756, MST-CINT, Los Alamos, NM 87545, USA.

Electronic address: kburch@lanl.gov

^†Permanent address: Department of Physics, California State University, East Bay, CA 94542, USA.

^‡Permanent address: Department of Physics, University of California, Riverside, CA 92521, USA

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Phys. Rev. Lett. 97, 087208 (2006) [4 pages]

Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor