Investigation of the electron--phonon interaction in Nb3Sn with the aid of microcontacts

The method of microcontact spectroscopy in the superconducting state was used to investigate weak nonlinearities of the current-voltage characteristics of point contacts made of Nb2Sn single crystals. The nature of the spectrum of the electron--phonon interaction was found to vary considerably from contact to contact, indicating considerable deviations of the composition of the surface of Nb3Sn from stoichiometry. A correlation was established between the nature of the spectrum and the magnitude of the gap singularities of the current-voltage characteristics. In the case of ''dirty'' high-resistance contacts with strong gap singularities the microcontact spectra were reasonably reproducible, which made it possible to relate them sufficiently closely to the microcontact function of the electron--phonon interaction in the bulk material. It was found that microcontact spectroscopy of this interaction was possible in the superconducting state not only in dirty S--c--S contacts, but also in dirty S--c--N contacts