REPRODUCIBLE INELASTIC TUNNELING IN NB BI2SR2CACU2O8+X POINT-CONTACT JUNCTIONS/

We discuss the reproducible dependence of tunneling conductance on vol tage in Nb/Bi2Sr2CaCu2O8+x (single-crystal) point-contact junctions. T he large and symmetric deviations from the background conductance obse rved at voltages greater than the gap are interpreted in the framework of inelastic electron tunneling at the surface of the high-temperatur e superconductor. The peaks of the odd second derivative of the tunnel ing current (d(2)I/dV(2))(odd), Shifted of the sum of Nb and Bi2Sr2CaC u2O8+x energy gaps, show a good correspondence with the peaks of the g eneralized phonon density of states G(omega) determined from neutron-s cattering data. The amplitude of the relative deviations of the conduc tance from the background is explained, as a first approximation, by m eans of inelastic tunneling at the surface of Bi2Sr2CaCU2O8+x assuming a large electron-phonon coupling strength lambda for selected phonon modes and, simultaneously, a small potential barrier U and a small thi ckness delta of the region where the inelastic process occurs.