Fluctuations and vortex-pattern ordering in the fully frustrated XY model on a honeycomb lattice -: art. no. 097003

The accidental degeneracy of various ground states of a fully frustrated XY model with a honeycomb lattice is shown to survive even when the free energy of the harmonic fluctuations is taken into account. The reason for that consists in the existence of a hidden gauge symmetry between the Hamiltonians describing the harmonic fluctuations in all these ground states. A particular vortex pattern is selected only when anharmonic fluctuations are taken into account. However, the observation of vortex ordering requires relatively large system size Lmuch greater thanL(c)greater than or similar to10(5).