The transistor is based on a design for a single-electron refrigerator that was unveiled earlier this year by Jukka Pekola and colleagues at the Helsinki University of Technology and NEST in Pisa, Italy (see Refrigerator cools one electron at a time).

Heat is transported by electrons as they tunnel though junctions between a metal and a superconductor (see figure). Only one electron at a time can squeeze through a tiny junction because mutual repulsion between electrons prevents multiple tunnelling. This orderly process ensures that only the hottest electrons can leave the metal, thereby causing heat to flow from the metal to the superconductor.

The researchers found that the heat flux though the transistor was a function of the temperature of the metal electrode, leading them to suggest that the device could be used as an accurate thermometer for measuring temperatures in the range of hundreds of millikelvin. Because the device allows for the precise study of the heat transported by single electrons, it could also help physicists to design better conventional electronic refrigerators, which also use electrons to transfer heat.

Pekola told Physics Web that while the heat transistor could someday be used to control the temperature of electronic devices, its very small cooling power rules out most practical applications.