Influence of Pb substitution in the charge reservoirs of Bi-2212 superconductors on pinning potential and superconducting properties

Doping at the charge reservoirs of cuprate superconductors has been shown to markedly enhance various superconducting properties. In this present study, a comprehensive comparative analysis has been conducted on the vortex states and pinning potential (U) in Bi${}_{2-x}$Pb${}_x$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ (x = 0, 0.5) superconducting samples. Although the pinning potential at zero temperature (U${}_0$) (estimated in the thermally activated flux flow (TAFF) model) decreases slightly upon doping, increased magnetic fields hardly affect U${}_0$ for the doped sample unlike the undoped one. This observation suggests lower degree of entanglement of vortex lines and reinforcement of plastic pinning by partial substitution of Pb ions in the Bi sites. Notably, upon doping Pb to Bi-2212 superconductor results in a significant broadening in its pinned vortex-liquid region, while retaining a high T${}_c$ value and this aspect has technological importance. Finally, an interesting vortex-phase diagram featuring diverse vortex states has been constructed from the magneto-transport measurement, for both undoped and Pb-doped samples.