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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.20: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

Dynamic large-N studies of impurity quantum phase transitions — •Matthias Vojta — Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, D-86135 Augsburg

Quantum impurity models exhibiting non-trivial critical behavior are investigated in a suitable large-N limit corresponding to a dynamic saddle-point. The resulting coupled integral equations can be solved exactly in the low-energy limit. In particular, we discuss a multichannel version of the pseudogap Kondo model, where a spin is coupled to a fermionic host with a power-law density of states near the Fermi level. This model displays a number of boundary quantum phase transitions, and is relevant for the physics of impurities in d-wave superconductors. Secondly, we study an impurity coupled to an antiferromagnet in its quantum paramagnetic phase. Near the bulk transition to the ordered state the impurity behavior becomes universal and is completely determined by spin gap and spin-wave velocity of the bulk system.