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TT: Tiefe Temperaturen
TT 30: Postersitzung IV: Kritische Ph
änomene, Quantenstörstellen, niederdimensionale Systeme
TT 30.10: Poster
Thursday, March 11, 2004, 14:30–19:00, Poster A
Ferromagnetic Polarons in the 2D Kondo Model — •Maria Daghofer1, Winfried Koller2, Hans Gerd Evertz1, and Wolfgang von der Linden1 — 1Institut für Theoretische Physik, TU Graz, Petersgasse 16, 8010 Graz, Österreich — 2Department of Mathematics, Imperial College London, London SW7 2BZ , GB
The 2D ferromagnetic Kondo model with classical corespins is studied via unbiased Monte-Carlo simulations. A canonical algorithm for finite temperatures is developed.
We show that with realistic parameters for the manganites and at low temperatures, the double-exchange mechanism does not lead to phase separation on a two-dimensional lattice but rather stabilizes individual ferromagnetic polarons. Within the ferromagnetic polaron picture, the pseudogap in the one-particle spectral function Ak(ω) can easily be explained.
Further, we explore the influence of the AFM superexchange coupling J′. We find that larger J′ stabilizes the polarons, while it destroys the ferromagnetism at very large doping and leads to the so called ”flux phase” around half filling of the lower Kondo band. We also find that lower temperatures further enhance polaronic behavior at realistic parameters J′ > 0.01.Detailed phase diagrams for β=50 and β=80 are given, in which a narrow window in parameter space exists for phase separation.