On-Chip Refrigeration by Evaporation of Hot Electrons at Sub-Kelvin Temperatures

Evaporation of hot electrons from a normal-metal into a superconductor can be used for efficient Peltier type cooling in micrometer size tunnel junctions. We have cooled the electrons to one third,¹ and, as the main result of the present paper, a separate silicon nitride membrane to about one half of its starting temperature; all results have been obtained at temperatures well below 1 K, where the lattice is weakly coupled to electrons thermally. The micromachined membrane can serve as a thermal bath for tiny samples, like bolometric radiation detectors in astronomy.