Role of mobile charge carriers and fluctuation induced conductivity in (Cu _0.5Tl _0.5-x K _x )Ba ₂Ca ₃Cu ₁Zn ₃O _12-δ Superconductor

The main role played by mobile carriers and fluctuation induced conductivity (FIC) in (Cu _0.5Tl _0.5-x K _x )Ba ₂Ca ₃Cu ₁Zn ₃O _12-δ (x=0, 0.25) superconductor samples are analyzed in the light of the Aslamazov-Larken (AL) theory. The enhancement of three-dimensional (3D) conductivity and grain size is achieved with K-doping at Tl sites in the (Cu _0.5Tl _0.5-x K _x )Ba ₂O _4-δ charge reservoir layer, which are further improved by post-annealing the samples in oxygen. The improvement of these factors causes the increase in cross-over temperature (T _o), zero resistivity critical temperature {T _c(R=0)} and T _c(onset) of diamagnetism to their higher values. We have also evaluated the exponents (λ _2D and λ _3D), zero temperature coherence lengths ξ _c(0), and interlayer coupling (J) for these samples and tried to correlate them to the superconductivity order parameters.