Inelastic tunneling of cooper pairs in c-direction in BSCCO single Josephson junctions and stacks

A reproducible fine structure at subgap voltages in the I(U)-characteristics of BSCCO single Josephson junctions and stacks has been observed and investigated. The structure is detectable only in the presence of an AC Josephson current. The overall form of the fine structure is in good agreement with the Raman scattering spectra of the optical phonon modes in this material. We attribute this structure to an inelastic (phonon assisted) tunneling of Cooper pairs, which is accompanied by the emission of coherent Raman-active optical phonons at resonance voltages U sub(res) identical with h omega sub(phon)/2e. The observed structure can be explained in terms of a theoretical model developed by Maksimov, Arseyev and Maslova.