Enhancement of Inter-plane Coupling and Superconductivity in Cu0.5Tl0.5Ba2(Ca3−yM y )Cu4O12−δ (M = 0, Pr, Y, Er, Gd; y = 0.02) Samples

Abstract

Cu0.5Tl0.5Ba2(Ca3−yM y )Cu4O12−δ (M=0, Pr, Y, Er, Gd; y=0.02) samples are synthesized at normal pressure to see the effect of M+3 elements doping in enhancing the inter-plane coupling of Cu0.5Tl0.5Ba2(Ca3−yM y )Cu4O12−δ superconductors. These samples have shown the tetragonal crystal structure in which the axis lengths increase with doping of rare-earth impurities. In the resistivity measurements, these samples have shown metallic variations of resistivity from room temperature down to the onset of superconductivity. The onset of superconductivity, the zero resistivity critical temperature, and the magnitude of diamagnetism are suppressed with the doping of rare-earth impurities at Ca sites. The excess conductivity analysis has shown suppression in the onset temperature of 3D and 2D Lawrence-Doniach (LD) conductivity regimes. The coherence length along the c-axis (ξ c(0)), the inter-layer coupling (J), and the Fermi velocity (V F) of the carriers are suppressed with Y doping, whereas the values of these parameters increase with the doping of Er and Gd. However, the values of B c0(T), B c1(T), and J c(0) are suppressed with the doping of Y, Er, and Gd. Moreover, the values of magnetic field penetration depth (λ pd) and the Ginzburg-Landau (GL) parameter κ increase with the doping of rare-earth elements. Since the λ pd is related inversely to the density of mobile carriers in the conducting CuO2 planes, the increase in values of these parameters indicates that the density of mobile carriers is suppressed in the conducting planes with the doping of rare-earth elements. These studies stress the pivotal role of mobile charge carriers in the mechanism of high- T c superconductivity and have shown that M+3 rare-earth elements develop some localization of the carriers in their neighborhood, thereby suppressing the values of essential superconductivity parameters.