Direct observation of the superconducting gap in phonon spectra
  We show that the superconducting energy gap $\Delta$ can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YNi$_2$B$_2$C demonstrates this new application of phonon spectroscopy. 
F. Weber, A. Kreyssig, L. Pintschovius, R. Heid, W. Reichardt, D.   Reznik, O. Stockert, K. Hradil