Cooling of electrons via superconducting tunnel junctions and their arrays exhibiting nodal lines

Abstract

We study theoretically a process of cooling electrons using a superconducting tunnel junction with a $π$ phase difference and a usual insulator or a ferroelectric in-between, and an array of such junctions with ferroelectric layers in-between. These setups have a complex structure of entropy due to nodal lines, where the density of states can be divergent or larger than for a free electron gas at a chemical potential level. We consider a small current running from the bath of electrons through the setup, where electrons have to have higher entropy, and thus remove heat from the bath.