It may be too small and impractical to keep a laptop cool, but a new microscopic transistor—the world's smallest human-made refrigerator--could help chill out x-ray sensors that probe cold dust and gas in the cosmos.
Today's transistors, like the ones arrayed on computer chips, depend on the flow of electrical current between thin layers of superconducting material. Functioning as so-called logic gates, they use a small bump in voltage to flip the flow of electrons on or off. The new transistor, in contrast, is the first of its kind to control heat flow.
Physicists at the Helsinki University of Technology in Finland, led by Jukka Pekola, designed a semiconductor in which electrons jump from the superconducting material onto a copper island in the transistor. Adjusting the voltage fine-tunes the energy levels of the electrons to a "sweet spot," allowing the more energetic, "hot" electrons to tunnel back to the superconductor material. Less energetic electrons remain behind on the copper island, which can cool to around 0.1 degrees Kelvin, the team reports in the 7 July Physical Review Letters. This temperature is a bit colder than the 0.3 Kelvin possible with helium-3 cooling, a standard cryogenic technique.
"The field of refrigeration at 0.1 Kelvin is very useful--certain sensors work very well at extremely low temperatures," says physicist Joel Ullom at the National Institute of Standards and Technology in Boulder, Colorado, because cold devices have less thermal noise to confound a signal. But Ullom says it's still a hot topic as to whether these tiny coolers will be able to join the larger refrigeration methods that are currently being used to cool astronomical detectors.
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