Effects of Pb substitution on the vortex state of oxygen-overdoped Bi2Sr2CaCu2O8+delta single crystal

We show that excessive Pb substitution of Bi in oxygen-overdoped BSCCO-2212 single crystal further reduces the anisotropy (rho(c)/rho(a) ratio) of the system in addition to enhancing disorder in its vortex system. These effec ts have led to the suppression of first-order vortex melting as well as a p eculiar second-peak effect exhibiting a sensitive temperature dependence ov er an unusually broad temperature range. Our-experimental data further reve al, in a Bi-based system, the presence of a disentangled vortex Liquid phas e separating the solid vortex from the entangled vortex liquid phase in the H-T diagram constructed from the transport and magnetization data.