Non-linear critical current thermal response of an asymmetric Josephson tunnel junction

TL;DR

This paper theoretically explores the non-linear thermal response of an asymmetric Josephson junction, revealing critical current jumps at specific temperatures and asymmetries, with potential applications in photon detection.

Contribution

It introduces a theoretical analysis of the critical current behavior in asymmetric SIS Josephson junctions under thermal bias, highlighting non-linear effects and potential detector applications.

Findings

Critical current exhibits jumps at certain temperatures when electrodes are asymmetrical.

Maximum current jump occurs at moderate asymmetry, r ≈ 3.

Behavior suggests potential for temperature-based single-photon detection.

Abstract

We theoretically investigate the critical current of a thermally-biased SIS Josephson junction formed by electrodes made by different BCS superconductors. The response of the device is analyzed as a function of the asymmetry parameter, $r=T_{c_1} /T_{c_2}$. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when $r\neq1$. In fact, in such case at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitively behaviour of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we found that the largest jump of the critical current is obtained for moderate asymmetries, $r\simeq3$. In view of these results, the discussed behavior can be speculatively proposed as a temperature-based threshold single-photon detector with photon-counting capabilities, which operates non-linearly in the non-dissipative channel.