Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 44: Poster Session Correlated Electrons

TT 44.86: Poster

Thursday, March 17, 2011, 10:00–13:00, P1

Optimized basis in continuous unitary transformations for symmetry-broken groundstates — •Nils A. Drescher and Götz S. Uhrig — Technische Universität Dortmund, Lehrstuhl für Theoretische Physik I, 44221 Dortmund, Germany

Continuous unitary transformations (CUT) [1,2] provide a generic, non-perturbative framework to derive effective low-energy models preserving the system’s symmetries. We use them to decouple and study low-lying magnetic excitations [3] of low-dimensional, antiferromagnetic spin 1/2 models. Our special focus is the quantum phase transition between disordered and long-range ordered phases with spontaneous staggered magnetization in two-dimensional dimerized systems. Introducing a variational parameter, the spin symmetry of the original quasiparticle basis can be broken, thus allowing the CUT to deal with a spontaneously symmetry-broken groundstate. Even in the magnetically disordered one-dimensional system, the optimal choice of the variation parameter allows for a gain of accuracy for magnetic properties.
C. Knetter, K.P. Schmidt and G.S. Uhrig, J. Phys. A: Math. Gen. 36, 7889 (2003)
S. Dusuel and G.S. Uhrig, J. Phys. A: Math. Gen. 37, 9275 (2004)
K. P. Schmidt and G.S. Uhrig, Phys. Rev. Lett. 90, 227204 (2003)