Determination of the electron-paramagnon coupling parameter of a transition metal from superconducting tunneling experiments

In a recent paper Burnell et al. presented a novel method of analysis for obtaining experimental estimates of the electron-phonon and electron-paramagnon coupling parameters lambda/sub ph/ and lambda/sub s/, respectively, for transition metals. Their analysis provides convincing evidence for strong paramagnon suppression of T/sub c/ in Nb and V. We show that this analysis can be improved by removing two unnecessary assumptions each of which can have a significant effect on the determination of lambda/sub s/. The experimental uncertainty in the estimate of lambda/sub s/ then depends primarily on uncertainties in the characteristic paramagnon frequency Ω/sub s/ and the usual Coulomb interaction parameter μ/sub ph/(. We calculate lambda/sub s/ for a reasonable range of values for these parameters and obtain estimates of lambda/sub s/ that are a factor of approx.2 larger than those of Burnell et al. for the same choice of μ/sub ph/( and Ω/sub s/approx.1 eV