Cooling, conductance and thermometric performance of non-ideal normal metal-superconductor tunnel junction pairs

摘要

We have investigated the effect of a difference in the tunnelling resistancesof the individual normal metal-insulator-superconductor (NIS) tunnel junctionsin a double junction SINIS device, with particular emphasis on the impact onthe conductance, cooling and thermometric performance. By solving theelectrical and thermal equations of the junctions in a self-consistent way, wefind that asymmetry gives rise to many new features, such as appearance of anexcess sub-gap current, improved cooling performance, exhibition of negativedifferential resistance, and improved temperature range of thermometricsensitivity. Experiments were also carried out to complement some of thenumerical results. In addition, we studied theoretically and experimentally theeffect of a finite series resistance, which also causes an excess current inthe subgap region, and a suppression of the conductance maxima at the gap edge.Experimental results agree well with the theoretical predictions.