Temperature-biased double-loop Josephson flux transducer

Abstract

We theoretically study the behavior of the critical current of a thermally-biased tunnel Josephson junction with a particular design, in which the electrodes of the junction are enclosed in two different superconducting loops pierced by independent magnetic fluxes. In this setup, the superconducting gaps can be modified independently through the magnetic fluxes threading the loops. We investigate the response of the device as a function of these driving magnetic fluxes, by changing the asymmetry parameter, i.e., the ratio between the low-temperature superconducting gaps δ = ∆10/∆20, and the temperatures of the system. We demonstrate a magnetically controllable step-like response of the critical current, which emerges even in a symmetric junction, δ = 1, and that depends on the different temperatures of the two electrodes. Finally, we discuss the optimal working conditions and the high response of the critical current to small changes in the magnetic flux, reporting good performances of the transducer, with a high transfer function that depends on the operating point and the quality of the junction.

Bipolar Thermoelectricity in Bilayer-Graphene/Superconductor Tunnel Junctions

“…However, it is worth noting that the possibility to tune the electrode gap is quite unique to this system. In fact in the SIS case one should change the material composing the electrode [28] or recurring to complex phase controlled gaps in proximised junctions [62].…”

“…|eV | (∆ R + ∆ L ), here ∆ R/L are the values of the bulk superconducting gap function on the two sides of the SIS' junction, therefore restoring the PH symmetry and suppressing the thermoelectric effect. This may be even more complex in out of equilibrium conditions since the Josephson coupling presents anomalous jumps when thermal gradients are applied to asymmetric SIS' superconducting junction [31,32]. Hence, the possibility of making a junction using instead a semiconductor coupled to superconductors would be beneficial in this respect.…”