Growth of (Cu0.5Tl0.5−x Hg x )Ba2Ca3Cu4O12−δ Superconductor with Optimal Carrier Density in CuO2 Planes and Fluctuation-Induced Conductivity

Abstract

The growth of (Cu0.5Tl0.5−xHgx)Ba2Ca3Cu4O12−δ (x=0, 0.25) superconductor with optimal carrier density in CuO2 planes has been made possible by partial substitution of Hg at Tl sites in (Cu0.5Tl0.5)Ba2O4−δ charge reservoir layer of (Cu0.5Tl0.5)Ba2Ca3Cu4O12−δ superconductor. The fluctuation-induced conductivity (FIC) analysis has been carried out on resistivity vs. temperature curves by using Aslamazov–Larkin (AL) theory and the results have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in order parameters. The microscopic parameters deduced from FIC analysis such as crossover temperature (To), zero temperature c-axis coherence {ξc(0)} and the interlayer coupling strength (J) have been improved with Hg substitution. Also, 3D region has been shifted to higher temperature with Hg substitution. In order to verify the optimal carrier density in CuO2 planes with Hg substitution, the post-annealing experiments have been carried out on these samples in nitrogen and air. These post-annealing experiments have caused under-doping of carriers from the optimal level resulting into a decrease in Tc (R=0) as well as the magnitude of diamagnetism.