Interplay of phase fluctuations and electronic excitations in high-temperature superconductors - A Monte Carlo simulation

Although the binding of electrons into Cooper pairs is necessary in forming the superconducting state, its remarkable properties like zero resistance and perfect diamagnetism require long-range phase coherence among the pairs as well. When coherence is lost due to thermal fluctuations of the phase at the transition temperature T,, pairing remains, together with short-range phase correlations. In conventional metals, Cooper pairs with short-range phase coherence are destroyed less than 1K above T-c. In underdoped high-T-c copper oxides, however there is spectroscopic evidence for some form of pairing up to a temperature T*, which is more than 100K above T-c. [1-3]. How this pairing above T, and Cooper-pair formation are related is one of the most challenging problems in high-T-c superconductivity. Here we report first numerical results of the dynamical properties of a model Hamiltonian which explicitly takes these phase-fluctuations into account by using a new Monte-Carlo (MC) technique. The phases are thereby controlled by a classical XY-action.