Jan Zaanen's article in this week's Nature (Nature v.448, p.1000; 30 August 2007) highlights an ArXiv preprint by Hartnoll et al. that seems to have made a connection between one aspect of String Theory called the anti-de-Sitter/conformal field theory correspondence(AdS/CFT), and the heat and charge transport in high-Tc superconductor called the Nernst effect.
Hartnoll et al. push what one might term the 'AdS-to-high-Tc correspondence' to its logical conclusion. They study its application to a particular, rather recondite transport phenomenon known as the Nernst effect — the crosswise flow of heat and charge currents in the presence of a magnetic field7 — in the nearly quantum-critical matter of a two-dimensional cuprate system. In a theoretical tour de force, they use the physics of a black hole in a three-dimensional anti-de-Sitter space that carries both electrical and magnetic charge to guide them in the very complex derivation of the relevant transport equations directly from quantum field theory. They show that these theoretical results are seemingly consistent with a number of hitherto unexplained features of the Nernst effect in a high-temperature superconductor7.
Man, that takes a lot of balls to do that! :) And what about the quark-gluon plasma that has been studied at RHIC?
Here, the AdS/CFT correspondence comes to the aid of the experimentalists in a similar way. The background is the observation that quark–gluon fireballs, as have been created in the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory on Long Island, behave in a remarkably simple way, but one that current theories find difficult to explain — they are governed by normal hydrodynamics, but have extremely low viscosity. Quite simply, the AdS/CFT correspondence tells us that when the quantum physics is scale invariant, the viscosity of such a system can be as small as it is. This result is far from obvious given our current understanding of quantum chromodynamics, the standard-model quantum-field theory of the strong nuclear force that governs interactions in the quark–gluon plasma.
I'm not going to jump onto the String Theory bandwagon and proclaiming it as the next best thing since sliced bread, but this is getting to be rather interesting.