Normal-metal∖insulator∖superconductor (NIS) junctions can be used as solid-state refrigerators since the hottest electrons preferentially tunnel from the normal metal into the superconductor. In this paper, we present NIS junctions optimized to cool electrons from a bath temperature of 100 mK. We measure a temperature reduction of the electrons in the refrigerator junctions from 100 to 26 mK which agrees with device models. Independent measurements of the electron temperature using thermometer junctions measure a temperature decrease from 100 to 48 mK. Theories explaining the difference in measured temperatures are discussed.
Citation: Journal of Low Temperature Physics
Pub Type: Journals
Microrefrigerators, Superconducting tunnel junctions