A QUANTITATIVE DESCRIPTION OF THE MICROWAVE PROPERTIES OF MELT CAST BI2SR2CACU2O8 IN TERMS OF A WEAK-LINK MODEL

The granular structure dominates the RF properties of the material. Be low T(c) the surface resistance at 11.27 GHz of Bi2Sr2CaCu2O8 drops in itially more slowly than BSC theory predicts. Below T(C)/2 it shows a linear temperature dependence and a quadratic frequency and field depe ndence 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 regi ons between crystallites, which provide a strikingly good description. The weak links with a boundary resistance R(bn) have to be regarded a s Josephson junctions with reduced superconducting properties and norm al conducting leakage currents. We conclude that the weak-link model g ives a consistent description of the DC and microwave properties not o nly in the magnitude of the penetration depth and surface resistance b ut also in their temperature, field and frequency dependence. Converse ly, it is possible to obtain from it quantitative information about we ak links in the superconductor Bi2Sr2CaCu2O8.