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

The phase transition ‘‘triangular lattice–vortex liquid’’ in layered highTc superconductors in the presence of pinning centers is studied. A two-dimensional system of vortices simulating the superconducting layers in a high-Tc 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 (.3 K! into islands which are pinned to the pinning centers and rotate around them and then, at a higher temperature (.8 K for Tc584 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 .2 K! and the temperature of the phase transition ‘‘rotating lattice–vortex liquid’’ increases substantially (.70 K!. © 1997 American Institute of Physics. @S0021-3640~97!01316-9#