Observed photon-assisted process in mesoscopic SNS mixers

The trajectory of quasiparticles in mesoscopic SNS weak-links is similar to the electron of hydrogen atoms. SNS weak-links are characterized by the Zener break down (tunneling) induced across the phase difference /spl phi/=/spl pi/ at large voltages. When the weak links are connected to a voltage bias source with zero output impedance, subharmonic gap structures are observed as a large dynamic resistance area or negative-differential conductance area at the voltage of V/sub n/=2/spl Delta//ne on the I-V curve. Where n=1,2,3..., strong structures are caused by resonance effect in between the energy gap and the multiple Andreev reflections that are present whenever there is a spatial inhomogeneity of pair potential. The enhanced IF signal peaks and their periodic modulation of voltage interval /spl planck//spl omega//e are observed around the subgap voltages. These results show rough profile of the density of states and a quantum structure due to photon-assisted process with the resonance effect in between the energy gap and the multiple Andreev reflections in SNS weak-links.