Tiny refrigerators have been made that reach temperatures as low as 0.1 kelvin. Joel Ullom at the National Institutes of Standards and Technology in Boulder, Colorado, and his colleagues at NIST and the University of Notre Dame in Indiana built the coolers from a sandwich of a metal, an insulator and a semiconductor.
As a result of the quantum tunnelling effect, applying a voltage to the sandwich forces energetic electrons to move out of the metal across the insulating layer and into the semiconductor. That cools the metal to extremely low temperatures. The team has managed to mount four coolers…
