Modification of current-voltage characteristics of double-barrier tunnel junctions under the influence of quasiparticle extraction

Enhancement of the magnitude of the value corresponding to the superconducting energy gap of Al' in Nb/Al-AlOx-Al'-AlOx-Al/Nb and Nb/Al/Nb/Al-AlOx-Al'-AlOx-Al/Nb/Al/Nb devices by tunnel extraction of quasiparticles has been investigated experimentally. The enhancement is observed both at the gap-difference and gap-sum voltage. In addition to the gap-difference and gap-sum features, there is a feature in the I-V characteristic which corresponds to the sum of the energy gaps of the external electrodes. The de and ac Josephson currents appear in the devices below the same critical temperature T-ceq, which is found to be T-ceq = 2.35 and 2.60 K for the devices of the first and second types, respectively. Below T-ceq, an enhancement of the dc component of ac Josephson current has been observed at V>0, as compared with the magnitude of the dc Josephson current at V = 0.