Abstract
We show evidence of a magnetic field dependent oscillation of subgap dynamic conductivity in a series of Nb–Al–AlOx–Al–Nb Josephson tunnel junctions in the voltage biased state. Our measurements show that the amplitude of conductance oscillations was maximum close to the subharmonic conductance peaks of the junctions, which are collective resonances of multiple Andreev reflected quasiparticles via pinholes in the tunnel barrier. The period of oscillations was commensurate with the macroscopic phase evolution of the junction. This observation suggests that under certain conditions practical Josephson tunnel junctions are analogous to Andreev interferometers, where the junction itself acts as the flux quantizer.
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