Friday, September 16, 2016

Another Case Where Electrons "Attract" Each Other

This is from a couple of months ago (hey, I'm kinda slow nowadays!), but what the hey....

So we all know (at least, I hope we all do) that the basic mechanism in conventional superconductors is the formation of Cooper Pairs. This is where two electrons in the material form an attractive coupling, which simply means that two electrons attraction each other. Despite the Coulomb repulsion between the two electrons, this attraction is due to the fact that the electrons live in a sea of phonons (lattice vibrations) that are formed by the positive ions of the material (or crystal lattice). So these phonons are the "glue" that bind these electrons together. Without them, two isolated electrons do not attract one another, obviously.

Now it seems that a long-proposed alternative mechanism of electron attraction has been confirmed. This time, two electrons attract each other not due to phonons, but due  to the repulsion of other electrons surrounding them. This is significant, and different than the phononic mechanism because this time, it is purely electronic in nature.

The original theoretical idea of such mechanism was first proposed by William Little[1], and the first experiment indicating its validity has been shown by Hamo et al,[2]. Certainly, there is an impetus to show if such electronic coupling could be a mechanism that leads to superconductivity. So far, none has been found. The Hamo et al., experiment decided to not deal with such complexity and just try to investigate first if such coupling would occur in the first place. So they did a nano-scale engineering design to show such a thing.

Very, very clever!

The big hurdle next is to find a material that can exhibit a similar effect.


[1] W.A. Little, Phys. Rev. 134, 1416 (1964),
[2] A. Hamo et al., Nature 535, 395 (2016).

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