Vortex phase diagram of Bi2Sr2CaCu2O8+y probed by critical Josephson current

To probe the vortex phase in Bi2Sr2CaCu2O8+y Single crystals in the field parallel to the c-axis, we have investigated the I-V characteristics of intrinsic Josephson junctions. Since the critical current I-c of junctions reflects the correlation of pancake vortices between the layers, the c-axis correlation of vortices could be probed by I-c measurements. In-line symmetric junctions fabricated by focused ion beam have been used to measure the I-V characteristics. An anomaly of I-c at the vortex lattice melting transition is actually observed at high temperatures. Additionally, other anomalies are also found by the field cooling measurements. The phase diagram obtained by I-c measurements is presented. (C) 2002 Elsevier Science B.V. All rights reserved.