Dresden 2009 – wissenschaftliches Programm

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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 6.2: Poster

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

Novel unitary transformations to treat systems with quasiparticles of finite lifetime — Tim Fischer¹, •Nils Drescher¹, Sebastian Duffe¹, and Götz S. Uhrig^1,2 — ¹Technische Universität Dortmund, Lehrstuhl für Theoretische Physik I, 44221 Dortmund, Germany — ²School of Physics, University of New South Wales, Kensington 2052, Sydney NSW, Australia

The method of self-similar continuous unitary transformations maps a given Hamiltonian to an effective Hamiltonian whose final structure depends on the generator of the unitary transformation. The aim is to derive an effective Hamiltonian simpler than the original Hamiltonian without losing its physics. One route is to disentangle sectors of different number of quasiparticles which is achieved by the MKU generator [1,2]. But this route fails if the elementary excitations have a finite lifetime due to hybridization with continua which is a common situation in physics.

We propose variants of the MKU generator and prove that they lead to converging flow equations. The new unitary transformations are tested and illustrated for one-dimensional spin models.

[1] A. Mielke, Eur. Phys. J. B 5, 605 (1998)

[2] C. Knetter, G.S. Uhrig, Eur. Phys. J. B 13, 209 (2000)