How Grain-Boundaries Influence the Intergranular Critical Current Density of Cu_(1-x)Tl_(x)Ba_(2)Ca_(3)Cu_(4)O_(12-delta) Superconductor Thin Films?

摘要

The insulating and metallic behavior of the grain-boundary weak links has been studied in thallium rich and the samples with small amount of thallium in the charge reservoir layer of Cu_(1-x)Tl_(x)Ba_(2)Ca_(3)Cu_(4)O_(12-delta) superconductor thin films. The influence of the nature of grain boundaries on the inter-granular critical current density (J_(c)) has also been investigated. From the power law dependence of H_(ac) approx (1 - T_(p)/T_(c))~(n), it was observed that n velence 1 gives a best fit for the J_(c) of thallium rich samples and n velence 2 provides a best fit for the J_(c) of the samples with small amount of thallium. The polycrystalline thin film samples showing the power law dependence of J_(c) as n velence 1 make superconductor-insulator-superconductor (SIS) type while the samples with n velence 2 follow superconductor-normal metal-superconductor (SNS) types of Josephson junctions. The insulating grain boundaries decrease the inter-granular Josephson coupling and hence the transport properties are suppressed.