Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 33: Low-dimensional Systems - Models II
TT 33.3: Vortrag
Freitag, 30. März 2007, 10:45–11:00, H18
Groundstates and thermodynamics of a highly frustrated spin model — •Andreas Honecker1, Daniel Cabra2, Hans-Ulrich Everts3, Pierre Pujol4, and Franck Stauffer5 — 1Institut für Theoretische Physik, Georg-August-Universität Göttingen, Germany — 2ULP Strasbourg, Lab. Physique Théorique, France — 3Institut für Theoretische Physik, Leibniz Universität Hannover, Germany — 4Lab. Physique Théorique, Université Paul Sabatier Toulouse, France — 5Institut für Theoretische Physik, Universität zu Köln, Germany
We consider a strongly trimerized kagomé lattice, as might be realized e.g. by fermionic atoms in optical lattices. For 2/3 filling, the chirality degrees of freedom of the individual triangles are governed by a pseudo-spin-1/2 Hamiltonian on a triangular lattice. According to previous studies, relevant aspects are captured by the classical version of this Hamiltonian. The properties of the model differ significantly for the different signs of the exchange constant. In one case, the groundstate is a 120∘ spin structure. Because of the discrete symmetry of the Hamiltonian we expect a finite-temperature ordering transition. In Monte Carlo (MC) simulations we measure specific heat, order parameter and the associated Binder cumulant. We determine the transition temperature and critical exponents. In the other case, which corresponds more closely to the kagomé antiferromagnet, the groundstates are macroscopically degenerate. A thermal order-by-disorder mechanism selects another 120∘ structure for the pseudo-spins, however only at very low temperatures. This phase transition is detected with MC simulations using the exchange method.