Thursday, November 22, 2007

'Cooper Pairs' Can Be Found In Insulators As Well Superconductors

This is a rather fascinating report. A team from Brown University has found evidence that Cooper Pairs can exist not just in a superconductor, but also in an insulator.

“Our finding is quite counterintuitive,” said James Valles, a Brown professor of physics who led the research. “Cooper pairing is not only responsible for conducting electricity with zero resis-tance, but it can also be responsible for blocking the flow of electricity altogether.”

However, unlike a superconductor, these Cooper pairs do not condense into a coherent state and, therefore, do not conductor electricity. It is interesting to note that this is similar to the behavior of the high-Tc cuprates in the pseudogap state. This is where one obtains a paring of the charge carriers ABOVE Tc. Here, no long-range coherence occurs even though pairing has occurred. Whether these paired carriers are precursor to superconductivity as the material goes below Tc, or are competing with superconductivity, is still a question yet to be answered.

Also interesting to note that this isn't the only situation where paring, and even superconductivity, can occur in an insulator. When an insulator shares a common surface with a superconductor, there is something call the proximity effect, whereby the superconducting wavefunction "leaks" into the insulator over some length (of the order of the the coherence length). What is different in this new work is that this pairing occurs on stand-alone insulator.

The exact citation to this work is:

M. D. Stewart, Jr. et al., Science v.318, p.1273 (2007).


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