title: Vortex patterns and infinite degeneracy in the uniformly frustrated XY models and lattice Coulomb gas.
abstract: We find analytically and numerically that there exist infinite degeneracies in the ground state vortex configurations of a uniformly frustrated XY model on a square lattice for cases of frustrations f=1/6, 1/7, 1/8, and 1/10. More generally, we could also obtain a class of exact solutions for the phase configurations corresponding to the cases of f=1/q=1/(2m) with an integer m>or=3 of which the above cases of m=3, 4, and 5 correspond to the true ground states. These states are analogous to the staircase solutions originally given by Halsey [Phys. Rev. B 31, 5728 (1985)], which, however, are relevant in a different regime of the frustration parameter (or vortex density). In these quasistaircase states, all the gauge-invariant phase differences are found to be integer multiples of pi/2q. The supercurrents are conserved at each node in a trivial manner by separate channels. The infinite ground state degeneracy is preserved in the case of an arbitrary screening length for the corresponding lattice Coulomb gas.
authors.affiliation: Department of Physics, Konkuk University, Seoul, Korea.
authors.forename: Myoung Kwan
authors.initials: MK
authors.lastname: Ko
authors.forename: Sung Jong
authors.initials: SJ
authors.lastname: Lee
authors.forename: Jooyoung
authors.initials: J
authors.lastname: Lee
authors.forename: Bongsoo
authors.initials: B
authors.lastname: Kim