Superconducting nonlinear thermoelectric heat engine

In a previous work, we predicted that a thermally biased tunnel junction between two different superconductors can display a thermoelectric effect of nonlinear nature in the temperature gradient under proper conditions. In this work we give a more extended discussion, and we focus on the two main features of the nonlinear contributions: (i) the linear-in-bias thermoelectricity, which can be associated to a spontaneous breaking of electron-hole symmetry, and (ii) the strong contribution at the matching peak singularity, which is typically associated to the maximum output power and efficiency. We discuss the nonlinear origin of the thermoelectricity and its relationship with the nonlinear cooling mechanism in superconducting junctions previously discussed in the literature. Finally, we design and characterize the performance of the system as a heat engine for a realistic design and experimental parameter values. We discuss possible nonidealities demonstrating that the system is amenable to current experimental realization.