Nonlinear Critical-Current Thermal Response of an Asymmetric Josephson Tunnel Junction

We theoretically investigate the critical current of a thermally biased superconductor-insulator-superconductor (S-I-S) Josephson junction formed by electrodes made from different Bardeen-Cooper-Schrieffer (BCS) superconductors. The response of the device is analyzed as a function of the asymmetry parameter, r=Tc1/Tc2. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when r≠1. In fact, in such a case, at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitive behavior of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we find that the largest jump of the critical current is obtained for moderate asymmetries, r≃3. 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 nonlinearly in the nondissipative channel.