Weak link behavior of superconductors

Abstract

A weak link behavior of(Cuo.sTlo.s)Ba2Ca2(Cu3-xSnx)OIO-o (x=O, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5) , superconductors were carried out which were synthesized by solid state reaction method. The crystal structure of these Sn doped samples is tetragonal and the axes lengths are found to increase with enhanced Sn doping concentration. The critical temperature and the magnitude of the diamagnetism are suppressed with enhanced doping of Sn. The samples turn into an insulator with very high room temperature resistivity if the Sn doping concentration is increased beyond y= 1.5. The decreased magnitude of diamagnetism with Sn doping is most likely arising from the decreased concentration of mobile carriers in the Cu02/Sn02 planes, which may suppress the Fermi-vector and superconducting parameters. The decreased concentration of mobile carriers is most likely arising from the localization of the carriers at the Sn +4 sites in the conducting Cu02/Sn02 planes. The carrier concentration in the conducting Cu02/Sn02 planes has been enhanced by carrying out post-annealing experiments in the air and oxygen atmosphere. These annealing experiments increase oxygen concentration in the (Cuos Tlo.s)Ba204_o charge reservoir layer, which stops the flow of free electrons in the conducting Cu02/Sn02 planes. The lower density of free electron in Cu02/Sn02 planes at room temperature lowers the electron hole recombination processes at lower temperature. Since holes are majority carriers in the superconducting state, therefore, the density of holes in the conducting CU02/Sn02 planes is enhanced with post-aJU1ealing in air and oxygen. The critical current densities of the samples are calculated by using Bean's critical field model. The Jc values so obtained are fitted to the power law behavior of the type (1- T/Tct of various values of n. Both the as prepared and oxygen post annealed samples gave a best fit for n=l for the superconductor insulator superconductor junction (SIS). This nature of material is due to oxide formation at the grain boundaries due to oxygen diffusion which possibly provide large surface areas to the shielding currents and enhance the Jc of the final compound.