Classical Phase Fluctuations in High Temperature Superconductors

Phase fluctuations of the superconducting order parameter play a larger role in the cuprates than in conventional BCS superconductors because of the low superfluid density ρₛ of a doped insulator. In this paper, we analyze an XY model of classical phase fluctuations in the high temperature superconductors using a low temperature expansion and Monte Carlo simulations. In agreement with experiment, the value of ρₛ at temperature T0ex0ex=0ex0ex0 is a quite robust predictor of Tc, and the evolution of ρₛ with T, including its T-linear behavior at low temperature, is insensitive to microscopic details.