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TT: Fachverband Tiefe Temperaturen

TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena

TT 6.38: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

Superperturbation solver for quantum impurity models — •Christoph Jung¹, Hartmut Hafermann¹, Sergey Brener¹, Mikhail Katsnelson², Alexei Rubtsov³, and Alexander Lichtenstein¹ — ¹I. Institute of Theoretical Physics, University of Hamburg, 20355 Hamburg, Germany — ²Institute for Molecules and Materials, Radboud University of Nijmegen, 6525 AJ Nijmegen, The Netherlands — ³Department of Physics, Moscow State University, 119992 Moscow, Russia

We present a very efficient solver for the general Anderson impurity problem. It is based on the perturbation around a solution obtained from exact diagonalization using a small number of bath sites. We formulate a perturbation theory which is valid for both weak and strong coupling and interpolates between these limits. Good agreement with numerically exact quantum Monte-Carlo results is found for a single bath site over a wide range of parameters. In particular, the Kondo resonance in the intermediate coupling regime is well reproduced for a single bath site and the lowest order correction. The method works directly on the real axis and thus allows to access the density of states without the need of analytical continuation of imaginary time data.