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${}^{\prime }$ in Nb/Al-AlO${}_x$-Al${}^{\prime }$-AlO${}_x$-Al/Nb and Nb/Al/Nb/Al-AlO${}_x$-Al${}^{\prime }$-AlO${}_x$-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 dc and ac Josephson currents appear in the devices below the same critical temperature $T_{\mathrm{c}\mathrm{}\mathrm{eq}},$ which is found to be $T_{\mathrm{c}\mathrm{}\mathrm{eq}}=2.35\mathrm{}$ and 2.60 K for the devices of the first and second types, respectively. Below $T_{\mathrm{c}\mathrm{}\mathrm{eq}},$ an enhancement of the dc component of ac Josephson current has been observed at $V>\mathrm{}0\mathrm{}$, as compared with the magnitude of the dc Josephson current at $V=0\mathrm{}$.