Andrea Pelissetto - La Sapienza, Roma
Interacting XY fields in two dimensions with an energy-energy coupling: numerical results
We consider a two-dimensional lattice model with two two-component scalar fields and with O(2)+O(2) symmetry. It should describe the criticalfluctuations in fully frustrated XY systems, for instance in the antiferromagnetic XY model on the triangular lattice. We identify two critical modes: one is associated with the breaking of the Z_2 symmetry related to the exchange of the two fields and the other is associated with the breaking of the continuous O(2) symmetry. Our simulationsshow that the two modes never become critical at the same temperature,except possibly at multicritical points.If the transition is unique, it is of first order, while in the oppositecase, if the transitions are both continuous, theybelong to the Ising and XY universality class respectively.Crossover phenomena are also discussed.
Joint work with Martin Hasenbusch and Ettore Vicari (Universita di Pisa).