Negative boron isotope effect of a ‘2Δ’ gap peak in Raman spectra from non-magnetic borocarbide superconductors Original Research Article

A hollow dielectric resonator technique has been developed for accurate measurements of the complex microwave surface impedance of novel superconductors from 2 to 20 GHz down to 100 mK. Illustrative measurements of the antiferromagnetic ordering and spin-dynamics of Gd ions in GdBa2Cu3O7 and of microwave penetration and losses in MgB2 wires and high quality single crystals of Sr2RuO4 are presented. Measurements on Sr2RuO4 imply an unchanged electron relaxation time τ on entering the superconducting state, a power law temperature dependence of the normal state fraction implying nodes in the superconducting order parameter, and residual low temperature losses on increasing frequency.