  We present simulation results on the equilibrium relaxation of Brownian
planar rotors based on a uniformly frustrated XY model on a square lattice. The
rotational relaxation exhibits typical dynamic features of fragile supercooled
liquids including the two-step relaxation. We observe a dynamic cross-over from
high temperature regime with Arrhenius behavior to low temperaure regime with
temperature-dependent activation energy. A consistent picture for the observed
slow dynamics can be given in terms of caging effect and thermal activation
across potential barriers in the energy landscapes.
