A quantitative description of the microwave properties of melt cast Bi2Sr2CaCu2O8 in terms of a weak-link model

Abstract

The granular structure dominates the RF properties of the material. Below Tc the surface resistance at 11.27 GHz of Bi2Sr2CaCu2O8 drops initially more slowly than BSC theory predicts. Below Tc/2 it shows a linear temperature dependence and a quadratic frequency and field dependence with an RF critical magnetic field of <130 A m-1 at 4.2 K. This behaviour is attributed to the existence of weak superconducting regions between crystallites, which provide a strikingly good description. The weak links with a boundary resistance Rbn have to be regarded as Josephson junctions with reduced superconducting properties and normal conducting leakage currents. We conclude that the weak-link model gives a consistent description of the DC and microwave properties not only in the magnitude of the penetration depth and surface resistance but also in their temperature, field and frequency dependence. Conversely, it is possible to obtain from it quantitative information about weak links in the superconductor Bi2Sr2CaCu2O8.