Two-stage melting of the vortex glass with strong point disorder

Abstract

We study the vortex phase diagram of Bi 2Sr 2CaCu 2O 8+δ in the presence of point like disorder, by using Monte Carlo simulation of the Lawrence-Doniach model. We found that the point-like disorder newly induces an intra-layer depinning transition as pre-melting, which subdivides the glass phase into two phases, from pinned-frozen glass (or Bragg glass at low-field) to weakly-pinned soft glass, when the temperature increases. This phase boundary makes an almost vertical line near 30 K. Subsequently, well above 30K, the intermediate glass melts into the pancake gas, implying a loss of interlayer long-range coherence. We also found a disorder-induced transition from three-dimensional Bragg glass to quasi-two-dimensional vortex glass, accompanied by an abrupt change of the interlayer coherence, with increasing field.