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TT: Fachverband Tiefe Temperaturen

TT 30: CE: Low-dimensional Systems - Models 1

TT 30.11: Vortrag

Donnerstag, 25. März 2010, 12:15–12:30, H20

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

Continuous unitary transformations (CUTs) [1,2] are a method to systematically derive effective models for many-particle-systems of finite or infinite size. They allow us to separate Hilbert spaces of different numbers of quasiparticles. We use them to study dimerized, antiferromagnetic spin 1/2 models. Our special interest is the quantum phase transition between spin liquid and long-range ordered phase with spontaneous staggered magnetization. To handle a spontaneously symmetry-broken groundstate with CUT, we modify the quasiparticle basis by introducing a continuous variation parameter. Even in the spin liquid phase, the optimal choice of this parameter leads to a significant gain of accuracy of magnetic properties. Results are shown for one and two dimensional systems.

[1] S. Dusuel and G.S. Uhrig, Journal of Physics A: Mathematics and General 37, 9275 (2004).

[2] C. Knetter, K.P. Schmidt, and G.S. Uhrig, Journal of Physics A: Mathematics and General 36(29), 7889 (2003).