Features of the melting dynamics of a vortex lattice in a high-T-c superconductor in the presence of pinning centers

The phase transition ''triangular lattice-vortex liquid'' in layered high-T-c superconductors in the presence of pinning centers is studied. A two-dimensional system of vortices simulating the superconducting layers in a high-T-c Shubnikov phase is calculated by the Monte Carlo method. It was found that in the presence of defects the melting of the vortex lattice proceeds in two stages: First, the ideal triangular lattice transforms at low temperature (similar or equal to 3 K) into islands which are pinned to the pinning centers and rotate around them and then, at a higher temperature (similar or equal to 8 K for T-c=84 K), the boundaries of the ''islands'' become smeared and the system transforms into a vortex liquid. As the pinning force increases, the temperatures of both phase transitions shift: The temperature of the point ''triangular lattice-rotating lattice'' decreases slightly (to similar or equal to 2 K) and the temperature of the phase transition ''rotating lattice-vortex liquid'' increases substantially (similar or equal to 70 K). (C) 1997 American Institute of Physics.