New superconductor ideas

Conundrum, Mon Aug 21 2006, 01:30PM

Hi all.

Seems that magnesium diboride only uses 3% of the available phonons (New Scientist 20/08/06)

It looks like there may be a way to use similar boride chemistry (Lithium borocarbide has been suggested) using a simple formula to get a material that superconducts at nearly 420K (i.e. more than the boiling point of water)



Thoughts on Why MgB2 is Such a Pathetic Superconductor
Warren E. Pickett
University of California Davis

The discovery of superconductivity at 40 K in MgB2 brought immediate amazement, which has not yet fully abated even though understanding of its mechanism has emerged quite rapidly. For phonon superconductors, MgB2 breaks all the "Matthias rules": it is not a transition metal compound, it does not have a large Fermi level density of states, and it is not cubic. Its seriously non-cubic structure is central to its success.

So while it is easy to marvel at MgB2 -- a remarkable high Tc class with only a single member -- it is provocative and perhaps useful to take the glass-half-full viewpoint: why isn't MgB2 a much better superconductor than it is? Why only 40 K, why not 75 K, why not room temperature?

I will address first the general characteristics that give rise to 40 K superconductivity, and extend the parameters in this class of materials to speculate about the maximum Tc such materials might support. At the simplest level this requires identifying structural instability arising from the ultrastrong el-ph coupling. Further considerations involve nonadiabaticity and anharmonicity. These questions will be considered within the context of the recently discovered superconductivity in B-doped diamond, which may be said to the second member of the MgB2 class (albeit three dimensional). "

-A