ELIASHBERG TREATMENT OF THE MICROWAVE CONDUCTIVITY OF NIOBIUM

High-precision microwave measurements have recently been carried out o n superconducting Nb samples. A BCS-like coherence peak has been obser ved below T(c). We find that a strong-coupling calculation of the micr owave conductivity, using electron-phonon spectral functions obtained from tunneling measurements, is unable to account for the height of th e peak. We also explain how, for microwave measurements at lower frequ ency, the height of the coherence peak can be used to provide informat ion about the low-frequency part of the electron-phonon spectral funct ion and the associated inelastic scattering rate.