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

Abstract

We show that excessive Pb substitution of Bi in oxygen-overdoped BSCCO-2212 single crystal further reduces the anisotropy $({\ensuremath{\rho}}_{c}/{\ensuremath{\rho}}_{a}$ ratio) of the system in addition to enhancing disorder in its vortex system. These effects have led to the suppression of first-order vortex melting as well as a peculiar second-peak effect exhibiting a sensitive temperature dependence over an unusually broad temperature range. Our experimental data further reveal, in a Bi-based system, the presence of a disentangled vortex liquid phase separating the solid vortex from the entangled vortex liquid phase in the $H\ensuremath{-}T$ diagram constructed from the transport and magnetization data.