Inhomogeneity of vortex charge in the 2D classical XY model

Microcanonical Monte Carlo simulations have been carried out on the 2D classical XY model which shows both Kosterlitz-Thouless (KT) as well as first-order transitions. Simulations on a 30 x 30 spin system show that the vortex charge distribution is inhomogeneous. The maximum inhomogeneity occurs at a temperature which coincides with the position of the specific heat peak in the KT case and in the coexistence region in the first-order case. The inhomogeneity is found to be larger in the KT case as compared to the first-order one. The vortices are found to be distributed in a more space-filling manner in the latter case as compared to the former one. (C) 1998 Elsevier Science B.V.