Schedule Nov 02, 2009
Infrared Optical Response of Ferromagnetic Semiconductors: Interplay Between Impurity Scattering and Dynamical Many-Body Effects
Carsten Ullrich (Univ. Missouri)

In III-V dilute magnetic semiconductors (DMS) such as GaMnAs, the transition-metal impurities are responsible both for providing mobile hole carriers and for inducing ferromagnetic transitions. This leads to rich and complex scenarios for optical and transport properties, where impurity scattering and many-body effects play an equally important role.

Most theoretical studies of transport and optical conductivity in DMS treat disorder and many-body effects within simple relaxation time and static screening models. Here we present a comprehensive theory of transport and optical response in charge and spin disordered media that combines a multiband k.p approach with a first-principles descriptions of disorder and electron-electron interaction through time-dependent density functional theory [1-3].

We discuss the effects of exchange-correlation, dynamic screening and collective electron excitations on the charge and spin scattering off Coulomb impurities and fluctuations of localized spins. We show that the exchange-correlation effects play an important role in the temperature dependence of dc-conductivity and that the pronounced drop in resistivity in the ferromagnetic phase is mostly due to scattering off the fluctuations of localized spins. A dynamic treatment of electron-electron interactions allows us to capture the collective excitations within the hole liquid, which substantially modifies the carrier scattering rate at finite frequencies. The so calculated infrared optical conductivities of GaMnAs compare well with experimental data [4].

This work was supported by DOE grant DE-FG02-05ER46213.

[1] F. V. Kyrychenko and C. A. Ullrich, cond-mat 0906.3526 (to appear in Phys. Rev. B)
[2] F. V. Kyrychenko and C. A. Ullrich, J. Phys.: Condens. Matter 21, 084202 (2009)
[3] F. V. Kyrychenko and C. A. Ullrich, Phys. Rev. B 75, 045205 (2007)
[4] E. J. Singley, K. S. Burch, R. Kawakami, J. Stephens, D. D. Awschalom, and D. N. Basov, Phys. Rev. B 68, 165204 (2003)

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