Just when we think that we know everything there is to know about conventional, metallic superconductors, Mother Nature throws a wrench at that fallacy. Reported today by Ayanajian et al., metallic superconductors such as Pb and Nb still holds a mystery. This time, it appears that the exact phonon energies of the Kohn anomalies happen to coincide with the superconducting binding energies of the cooper pairs of that particular metal. This is something that was not expected, and current formalism of conventional superconductivity says nothing about such a thing. As Scalapino pointed out his is Perspective article,
... although the polarization created by the conduction electrons and the response to the ionic lattice contribute to determining both the Kohn anomaly and the pair binding energy, there must be something else at work that locks (the superconducting gap) to (Kohn anomaly energy). As noted, this could mean that there is some new physics that is not captured by the Eliashberg formulation.
I love it! I love unexpected surprises like this!
 P. Ayanajian et al., Science v.319, p.1509 (2008).
 D.J. Scalapino, Science v.319, p.1492 (2008).