Phase diagram for a generalized fully frustrated triangularXYmodel

Abstract

To better understand the phase diagram for XY spins on the fully frustrated triangular lattice, we generalize that model, giving one class of bonds a ‘‘tunable’’ strength -ηJ, where η=1 gives the conventional model. As a consequence, the sites are no longer all equivalent. Using mean-field theory, the phase diagram has been determined as a function of η, the applied field H, and the temperature T. For H=0, the phase diagram is very similar to that for the generalization of Berge et al. of the fully frustrated XY square lattice model. For H≠0 and -0.51 the extension of the paramagnetic phase is absent. For η=1 we conclude that the simplest explanation for the Potts phase can be obtained by comparison to the Monte Carlo phase diagram for Ising spins on this lattice.