Low Temperature Characteristics of the Metal–Superconductor NIS Tunneling Thermometer

Abstract

We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.

Ultimate Accuracy of Frequency to Power Conversion by Single-Electron Injection

“…Besides the influence of driving frequency, deviations from the ideal P ¼ 2fΔ arise from temperatureindependent subgap leakage and from nonvanishing temperature that were ignored above. For the first one, we assume the standard Dynes form of the DOS [17,18] n S ðϵÞ ¼ jRe½ðϵ þ iγÞ= ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi ðϵ þ iγÞ 2 − 1 p j, with the dimensionless smearing parameter γ, which can be directly related to experimental parameters [19]. To obtain the average heat in a half-period, we follow the same procedure as before, but now with the subgap DOS n S ðϵÞ≈ γ=ð1 − ϵ 2 Þ 3=2 for jϵj < 1 and subsequent survival PHYSICAL REVIEW LETTERS 129, 037702 (2022) 037702-2 probability pð1Þ ¼ e −γ=Ω .…”