Calculation of point-contact characteristics for normal metals without and with impurity scattering

Point-contact current-voltage characteristics have been calculated using a Debye model for phonons and a spherical Fermi surface with the theory of Kulik et al. (1977). The authors find that the constriction spectral function has a peak at the same energy as the phonon density of states and alpha 2F (the tunnelling spectral function), but that the peak is much narrower for the constriction spectral function. If Umklapp scattering were to be included, this would tend to broaden the peak. With two Debye peaks in the calculation, the relative strengths of the two peaks in the constriction spectral function are different from those in alpha 2F. The authors have extended the Kulik theory to include impurity scattering in the relaxation-time approximation. Impurity scattering tends to broaden the peak in the constriction spectral function; in this approximation it does not produce a background.

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