Point contact spectroscopy of superconductors with a strong electron–phonon interaction

It is shown that as in the case of tunnel junctions, the nonlinearity of the current–voltage characteristics (IVC) of superconducting point contacts can be used to obtain the dependence of the order parameter on energy and to reconstruct the electron–phonon interaction (EPI) function through an inversion of the Eliashberg equations. The effect of the electron spectrum renormalization due to EPI on the steady-state IVC of an S–c-N contact is studied. This effect leads to a nonlinear conductivity which is manifested in the form of peaks in the region of characteristic phonon energies. The correction to the point-contact current, which is a manifestation of the elastic scattering of electrons by nonequilibrium phonons generated by the electron flow in the region of a microconstriction, is determined: The correction fixes the phonons near the Van-Hove singular points on the phonon spectrum.

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