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Science 17 December 1999:
Vol. 286. no. 5448, p. 2229
DOI: 10.1126/science.286.5448.2229a
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This Week in Science

Particles can be made to move in one direction by applying a time-varying asymmetric potential. For proteins and small molecules, these "ratchets" act classically, but quantum-mechanical effects have been predicted for particles that can tunnel through their potential barriers. One manifestation is that the ratchet would reverse the net direction of particle flow as a function of temperature. Linke et al. (p. 2314) have now verified this effect experimentally for electron flow in a semiconductor heterostructure and present a simple model that explains why current reversals occur.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)