Quantum point contacts (here the channel is a fraction of a micron wide) show an unusual pattern of conductance that has so far defied explanation. Theoretical work supports a recent interpretation, even as experimental data seem to shore up an old standard.
Image credit: K. Ensslin et al./ETH Zürich
Researchers continue to push rival interpretations of a vexing problem in mesoscopic physics, the size scale where quantum and classical worlds co-exist. The conductance across a narrow bridge between two reservoirs of electrons--a so-called quantum point contact--was expected to follow simple quantum rules, but doesn't. A group recently proposed a model of automatic electron spin alignment to explain the conductance anomaly. But a different group's theory supports the claim that physics concepts borrowed from the world of material impurities is key. Both teams hope they're approaching a resolution to a problem that has turned mesoscopic physics on its head.