Flux Dynamics and Vortex Phase Diagram in Tl2Ba2CaCu2O8 Thin Films

By doing sensitive magnetic measurement, the current-voltage ( I-V or E-j ) characteristics were determined for Tl2Ba2CaCu2O8thin films at temperatures between 4.2 K and 70 K in magnetic fields up to 6T. We found a crossover of the dimensionality of flux dynamics from 3D at low fields to 2D at high fields. The vortex matter melts at a finite temperature at a low field ( 3D ) and at zero K at a high field ( 2D ). Finally we attempt to give a vortex phase diagram based on this analysis.