A Finnish group of researchers at the Low Temperature Laboratory of Helsinki University of Technology (TKK) have developed and fabricated a nanoscale heat transistor, and simultaneously the smallest refrigerator ever made.

The device, nanofabricated with the help of electron beam lithography, functions at extremely low temperatures of less than one degree above absolute zero. The possibility to control the electrons going through the device one by one in the metal-superconductor structure enables its use as a heat transistor.

The electron coolers could be used in the future, for instance, in space research for the precise cooling of tiny radiation detectors, and the small size and simplicity of the device may prove valuable in other areas of research as well. Other areas of application may include, for instance, sensors used in imaging.

The heat transistor has been developed and fabricated as a collaborative project between the TKK Low Temperature Lab and the Italian Scuola Normale Superiore.

Olli-Pentti Saira, Matthias Meschke, Francesco Giazotto, Alexander M. Savin, Mikko Möttönen, and Jukka P. Pekola, Heat Transistor: Demonstration of Gate-Controlled Electron Refrigeration, Physical Review Letters 99, 027203 (2007).