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TT: Fachverband Tiefe Temperaturen

TT 52: CE: Low-dimensional Systems - Models 1

TT 52.2: Vortrag

Donnerstag, 17. März 2011, 14:15–14:30, HSZ 105

Disordered groundstate phase for 2D-lattice models of hard-core bosons — •Ansgar Kalz, Andreas Honecker, Sebastian Fuchs, and Thomas Pruschke — Institut für Theoretische Physik, Universität Göttingen

We present Quantum Monte-Carlo data for frustrated models on 2D-lattices. The spin-1/2-Heisenberg model with antiferromagnetic S^z-interaction and ferromagnetic interactions in the x-y–plane can be rewritten as model of hard-core bosons with repulsive density-interactions. Longer-range interactions, i.e., next-nearest neighbor interactions introduce frustration for the square lattice as well as for the hexagonal lattice. Depending on the strength of the frustration we find different classical groundstates which are seperated by a critical point. The frustration yields a large degeneracy that hinders the classical ordering process in the vicinity of the critical point.

For the square lattice with nearest neighbor and competing next-nearest neighbor interactions we calculated magnetic observables and higher-order correlation functions. We show finite temperature phase diagrams and the groundstate phase diagram where we identified a finite region without any order.

On the honeycomb lattice we included interactions up to third nearest neighbors and find a similar scenario as for the frustrated square lattice. In the vicinity of the ciritical point of the model we find a region without classical order and present measurements of higher-order correlation functions.