Classical phase fluctuations in high temperature superconductors

Phase fluctuations of the superconducting order parameter play a larger rol e in the cuprates than in conventional BCS superconductors because of the l ow superfluid density rho(s) of a doped insulator. In this paper, we analyz e an XY model of classical phase fluctuations in the high temperature super conductors using a low temperature expansion and Monte Carlo simulations. I n agreement with experiment, the value of rho(s) at temperature T = 0 is a quite robust predictor of T-c, and the evolution of rho(s) with T, includin g its T-linear behavior at low temperature, is insensitive to microscopic d etails.