Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 47: Correlated Electrons: Spin Systems and Itinerant Magnets 2
TT 47.11: Vortrag
Freitag, 30. März 2012, 12:15–12:30, H 0104
Critical scales in anisotropic spin systems from the functional renormalization group — •Stefan Göttel1,2, Sabine Andergassen1,2, Dirk Schuricht1,2, Carsten Honerkamp2,3, and Stefan Wessel3,4 — 1Institute for Theory of Statistical Physics, RWTH Aachen — 2JARA-Fundamentals of Future Information Technology — 3Institute for Theoretical Solid State Physics, RWTH Aachen — 4JARA-High-Performance Computing
We apply a recently developed functional renormalization group scheme [Reuther et. al, Phys. Rev. B 81, 144410 (2010)] for quantum spin systems to the spin-1/2 antiferromagnetic XXZ model on a two-dimensional square lattice. Based on an auxiliary fermion representation we derive flow equations which allow a resummation of the perturbation series in the spin-spin interactions. This way, the spin susceptibilities are calculated for different values of the anisotropy parameter, confirming the phase transition between planar and axial ordering at the isotropic point. As recently proposed in [Reuther et. al, Phys. Rev. B 84, 100406(R) (2011)], we extract critical temperatures from the flow. In the Ising limit these results coincide with the Onsager solution, but violate the Mermin-Wagner theorem at the isotropic point and a satisfactory description of the behavior in the vicinity of the phase transition is not possible. A quantitative comparison with quantum Monte-Carlo shows major differences. We trace this problem back to an incorrectly generated selfenergy and discuss potential improvements.