Dresden 2003 – scientific programme

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TT: Tiefe Temperaturen

TT 11: Postersitzung II (Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen, Theorie: Systeme korrelierter Elektronen)

TT 11.21: Poster

Tuesday, March 25, 2003, 14:30–19:00, P2c, P2d

The projection-operator approach to the Kondo-lattice model — •Tilmann Hickel and Wolfgang Nolting — Humboldt-Universität, Institut für Physik, Festkörpertheorie, Invalidenstr. 110, 10115 Berlin

Whenever the coupling of localized magnetic moments to a band of itinerant conduction electrons dominates the physical properties of a material, the Kondo-lattice model (including Zener’s double-exchange picture) is a good choice for a theoretical treatment. That is especially the case for diluted magnetic semiconductors [e.g. (Ga_1−xMn_x)As], manganites [R_1−xA_xMnO₃] and classical local moment systems [EuO, EuS, Gd]. Till now approaches to this model have the property to be non-perturbative, to be not fully self-consistent or to treat the spin operators classically.

We propose to use the projection-operator method, as introduced by Mori, for a more general analytical approach to the Kondo-lattice model. The method has been successfully tested for several exactly known limiting cases. We have derived an expression for the self-energy which is correct up to second order in the coupling parameter, have improved the result within the scheme of a modified perturbation theory and examine the accuracy of the obtained densities of states. It turns out that the projection-operator method is able to retrieve known features of the Kondo-lattice model and has the potential to go beyond.