Nonlinear critical current thermal response in an asymmetric Josephson tunnel junction: the Josephson threshold calorimeter

We discuss the peculiar behavior of the critical current Ic, that is the maximum supercurrent that can flow in the device, of a temperature-biased Josephson tunnel junction formed by different superconductors[1]. Our theoretical exploration ofcoherent thermal transport in such a junction reveals the abrupt variation of Ic as the electrodes forming the device reside at specific temperatures. In particular, we thoroughly discuss a counterintuitively non-linear behavior of the critical current, since it increases by enhancing the temperature of one lead, instead of monotonically reducing as naively expected. This phenomenon paves the way to the use of an asymmetric Josephson junction as a temperature-based threshold single-photon detector operating in the non-dissipative branch.[2] This device is conceived to work at temperatures slightly lower than those giving a critical current sudden jump, so that an incident photon can be easily revealed since it produces a temperature increase that can induce a clearly measurable critical current variation.

Alessandro Braggio - <a href="mailto:alessandro.braggio@nano.cnr.it