Reversibility Of Superconducting Nb Weak Links Driven By The Proximity Effect In A Quantum Interference Device

Abstract

We demonstrate the role of the proximity effect in the thermal hysteresis of superconducting constrictions. From the analysis of successive thermal instabilities in the transport characteristics of micron-size superconducting quantum interference devices with a well-controlled geometry, we obtain a complete picture of the different thermal regimes. These determine whether or not the junctions are hysteretic. Below the superconductor critical temperature, the critical current switches from a classical weak-link behavior to one driven by the proximity effect. The associated small amplitude of the critical current makes it robust with respect to the heat generation by phase slips, leading to a nonhysteretic behavior.

Controlling hysteresis in superconducting constrictions with a resistive shunt

“…These transitions have been seen reproducibly in three different devices and are attributed to the thermal instability of N-S interface in different superconducting portions. The magnitude of I r2 agrees with the instability current in 2 µm wide leads [8]. All the five retrapping currents follow similar square-root dependence on (T c − T b ) as expected for the instability currents [8].…”

“…The magnitude of I r2 agrees with the instability current in 2 µm wide leads [8]. All the five retrapping currents follow similar square-root dependence on (T c − T b ) as expected for the instability currents [8].…”

“…The extrapolated critical temperature T c close to 7.2 K is that of the WL itself. In both the devices, the critical current I c decays markedly slower above T h or T hs , owing to the proximity effect [8].…”

“…At low temperatures, sharp voltage jumps and drops are observed at the critical current I c and at two re-trapping currents I r1 and I r2 . The latter two arise from thermal instabilities respectively in the WL plus the narrow leads (I r1 ) and in the wide leads (I r2 ) [8]. At 1.3 K, I c is higher than both I r1 and I r2 [see Fig.…”

“…The extrapolated critical temperature T c close to 7.2 K is that of the WL itself. In both the devices, the critical current I c decays markedly slower above T h or T hs , owing to the proximity effect [8].The retrapping current I r1 follows a similar temperature dependence in the two devices but with a higher magnitude, by a factor of about 1.64, in the shunted device. This factor is similar to that found from Eq.…”