Wednesday, July 20, 2011

Bristol physicists break 150-year-old law

Bristol physicists break 150-year-old law: In 1996, American physicists C. L. Kane and Matthew Fisher made a theoretical prediction that if you confine electrons to individual atomic chains, the Wiedemann-Franz law could be strongly violated.  In this one-dimensional world, the electrons split into two distinct components or excitations, one carrying spin but not charge (the spinon), the other carrying charge but not spin (the holon).  When the holon encounters an impurity in the chain of atoms it has no choice but for its motion to be reflected.  The spinon, on the other hand, has the ability to tunnel through the impurity and then continue along the chain.  This means that heat is conducted easily along the chain but charge is not.  This gives rise to a violation of the Wiedemann-Franz law that grows with decreasing temperature.
The experimental group, led by Professor Nigel Hussey of the Correlated Electron Systems Group at the University of Bristol, tested this prediction on a purple bronze material comprising atomic chains along which the electrons prefer to travel.
Remarkably, the researchers found that the material conducted heat 100,000 times better than would have been expected if it had obeyed the Wiedemann-Franz law like other metals.

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