Flipping-Coin Experiment to Study Switching in Josephson Junctions and Superconducting Wires

Abstract

When probed with current pulses, Josephson junctions and superconducting wires exhibit stochastic switching from a superconducting to a stable nonzero-voltage state. The electrical current dependence of the switching probability (the so-called S curve) or the switching-current distribution is a fingerprint of the physics governing the escape process. This work addresses the criterion of the independent switching event, which is important for the credibility of the switching measurements of superconducting wires and various Josephson junctions involving superconductor-insulator-superconductor tunnel junctions, proximity junctions, and Dayem nanobridges. Treating the Josephson junction as an electrical coin with a current-tuned switching probability, we investigate the effect of correlation between switching events on the switching statistics. We show that such a correlation originates from the thermal dynamics of the superconducting wire.

Stochastic thermal feedback in switching measurements of a superconducting nanobridge caused by overheated electrons and phonons

“…V of the Ref. [23]. For completeness of our presentation we analyze these data once again in the current paper, introducing as a new element quantification of the phonon overheating due to a single switching event.…”

“…3(c)]. This relaxation is governed by electron-phonon coupling and by hot-electron diffusion [22,23]. Both energy-relaxation channels bring electrons into thermal equilibrium with phonons.…”

“…The independent switching experiments manifest themselves in the binomial distribution of switchings for a fixed value of the probing current: JJ behaves like a coin for which the head and tail experiment is performed [23]. By virtue of independence the switching probability is not affected by the outcome of the probing in any other pulse.…”

Heat Hunting in a Freezer: Direct Measurement of Quasiparticle Diffusion in Superconducting Nanowire

“…We use and further develop nanosecond thermometry based on stochastic switching of a Josephson junction from superconducting to normal state [16,34]. A particular type of Josephson junction, a superconducting aluminum nanobridge known in the literature as the Dayem bridge, is well tailored for tracing rapid changes in temperature, which are expected when hot electrons propagate across the nanostructure.…”

“…Collection of P(I test ) dependences at different temperatures gives knowledge of δP/δI test and dI sw /dT e , and allows us to calculate the temperature responsivity at constant testing current amplitude ( P/ T e ) I test . The uncertainty in T e determination is set by accuracy of probability measurement [34], that is P un = [P(1 − P)/N ] 1/2 (N is number of pulses) and reads T e,un = (−δP/δI test × dI sw /dT e ) −1 P un . The method is applicable only for linear regime when P ∼ T e .…”