RESISTIVITY MEASUREMENTS AND THE VORTEX PHASE-DIAGRAM OF BI2SR2CACU2OY

We have measured We temperature dependence of the ab-plane resistivity on Bi2Sr2CaCu2Oy single crystals with high sensitivity. A clear resis tivity drop was observed when a relatively lour magnetic field was app lied, which is attributed to the melting transition of the flux line l attice. Three crystals with different carrier doping level were invest igated and the phase diagrams are determined from the resistivity meas urements. It is also shown that the phase transition temperature depen ds strongly on the angle between the magnetic field and the crystallog raphic c-axis direction, reflecting the large anisotropy of Bi2Sr2CaCu 2Oy.