Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 12: Correlated Electrons: Spin Systems and Itinerant Magnets 2

TT 12.2: Vortrag

Montag, 23. März 2009, 14:15–14:30, HSZ 304

Dynamic Spin Excitations and Magnetism in the Hubbard Model — •Sebastian Schmitt — Lehrstuhl für Theoretische Physik II, TU Dortmund

The static and dynamic magnetic susceptibility of the Hubbard model is calculated within the dynamical mean field theory (DMFT) using the enhanced non-crossing approximation (ENCA) as impurity solver. The magnetic properties are discussed for various dopings, temperatures and lattices with and without frustration. Special emphasis is laid on the interpretation in terms of the two fundamental pictures of magnetism, i.e. Stoner-type magnetism of itinerant electronic excitations and Heisenberg spin-magnetism of localized magnetic moments. The transition between these two opposing pictures is discussed. An interesting reentrant behavior is observed for the antiferromagnetic Néel temperature in the intermediate coupling region. Additionally, a dispersionless collective mode is observed in the dynamic magnetic susceptibility for large values of the Coulomb repulsion at very low temperatures, indicating a localized singlet-triplet excitation connected with the breakup of local Kondo-singlets.