3 ms·

Big mystery holding back practical superconductors may have been solved.

8 points by aresant 16y ago

sophacles 16y ago
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).
gjm11 16y ago
Brookhaven press release: http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1155 http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1155 Nature article: http://www.nature.com/nature/journal/v466/n7304/full/nature09169.html http://www.nature.com/nature/journal/v466/n7304/full/nature0... PDF of article: http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Nature_466_347.pdf http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Natur... 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.)

8 points by aresant 16y ago

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).

gjm11 16y ago

Brookhaven press release: http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1155 http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1155 Nature article: http://www.nature.com/nature/journal/v466/n7304/full/nature09169.html http://www.nature.com/nature/journal/v466/n7304/full/nature0... PDF of article: http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Nature_466_347.pdf http://people.ccmr.cornell.edu/~jcdavis/publicationPDF/Natur... 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.)