Phonon structure of unusually high energy and strength in Nb-Nb oxide-Pb tunnel junctions

Tunneling measurements on Nb-Nb oxide-Pb junctions with barriers formed by rf oxidation reveal phonon modes contributing to the superconducting pair potential Δ(E) at E=115 meV. This structure is interpreted as resulting from vibrations of Nb-O octahedra in an interfacial layer of Nb2O5 in which superconductivity is induced by proximity with Nb. © 1983.