Macroscale refrigeration by nanoscale electron transport

We demonstrate a general-purpose solid-state refrigerator for sub-Kelvin temperatures based on the tunneling of hot electrons through normal-metal/insulator/superconductor (NIS) junctions. Previous devices using this cooling principle fell short of general-purpose refrigerators since they could not be coupled to arbitrary payloads. To create a viable refrigerator, we developed optimized NIS structures and techniques to couple multiple such structures to arbitrary objects. Using three linked NIS devices, we reduced the temperature of a 1.9 cm3 copper stage from 290 mK to 256 mK with 700 pW of cooling power at 290 mK. We present plans to achieve base temperatures near 100 mK.