Comment on Tunneling α2F(ω) from sputtered thin-film NbN

Certain disadvantages of the choice of the material of the counterelectrode and hence the inadequacies of the results of the paper on tunneling α2F(ω) from thin-film NbN by Kihlstrom, Simon, and Wolf [Phys. Rev. B 32, 1843 (1986)] are pointed out, and suggestions are made to improve upon the present results. Pb is not an ideal choice as a counterelectrode material because the electron-phonon interaction in Pb is strong and this can manifest itself in the tunneling characteristics even if the superconductivity in Pb has been quenched by the application of a magnetic field. An ideal choice would be a BCS superconductor (preferably Al) and the data should be taken with both the electrodes in the superconducting state to avoid thermal broadening effects in the normal state. Contribution of the Al density of states can be taken care of by the deconvolution of the integral for the normalized conductivity of the junction