Point-contact spectroscopy of electron-phonon interaction in   superconductors
  The possibility to reconstruct the electron-phonon interaction (EPI) function was demonstrated for S-c-N and S-c-S point contacts using the superconducting inelastic contribution to the excess current caused by Andreev reflection processes. Superconductors with both weak (Sn, Al) and strong (Pb, In) EPI were considered. It was shown that in the latter case it is necessary to account for the elastic component of current which is related to the frequency dependence of the superconducting energy gap arising due to electron-phonon renormalization of the energy spectrum of the superconductor. 
N. L. Bobrov, A. V. Khotkevich, G. V. Kamarchuk, and P. N. Chubov
cond-mat.supr-con