J. Halbritter, Comment on "Direct observation of the superconducting energy gap developing in the conductivity spectra of niobium", PHYS REV B, 60(17), 1999, pp. 12505-12506
For Nb-surface impedance measurements, various deviations from BCS and Elia
shberg theory have been reported. Those claimed deviations from theory are
instead related to chemistry, i.e., by taking the Nb-O reaction properly in
to account. [S0163-1829(99)00642-6].