

Big mystery holding back practical superconductors may have been solved. - aresant
http://io9.com/5588366/big-mystery-holding-back-practical-superconductors-may-have-been-solved

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gjm11
Brookhaven press release:
<http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1155>

_Nature_ article:
[http://www.nature.com/nature/journal/v466/n7304/full/nature0...](http://www.nature.com/nature/journal/v466/n7304/full/nature09169.html)

PDF of article:
[http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Natur...](http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Nature_466_347.pdf)

So, if I'm understanding right, here's what's going on. They're working with a
Bi-Sr-Ca-Cu-O superconductor. The structure of this has planes that basically
consist of layers of copper oxide, arranged in a square lattice. The CuO2
units are symmetrical: there's no obvious difference between the two oxygen
atoms. In the superconducting phase (at low temperatures) the distribution of
electrons (er, strictly, something to do with the electron wavefunction -- all
sorts of weird collective quantum effects happen in superconductors) is
likewise symmetrical; likewise at high temperatures where of course there's no
superconductivity because thermal motion breaks up all the coherent things
that need to happen for superconductivity.

When the temperature is a bit too high for superconductivity, the mechanism by
which superconductivity fails seems to be this: the electrons have enough
energy to get into a state called the "pseudogap state", which interferes in
some manner -- which I don't understand -- with superconductivity. The
pseudogap state is not well understood.

These people have found out something interesting about what happens to
electrons in these pseudogap states: that symmetry is broken. For each copper
atom, the electron density is much greater near one of the associated oxygen
atoms than near the other. (They measure this with a scanning tunnelling
electron microscope.) _Which_ oxygen atom wins may be different for different
copper atoms, but it appears that as the energy of the electrons increases, so
does the length-scale on which the answer is consistent -- i.e., the size of
the structured electron density variations this produces.

(I'm not really a physicist, and certainly not a superconductor expert. Any of
the above may be entertainingly wrong. Corrections welcome.)

------
sophacles
Can anyone explain this a bit deeper, or point to a resource that does? I find
these dumbed down articles more confusing than stuff full of precise jargon
(even if i know nothing of the jargon, at least it usually isn't some weak
analogy with big holes).

