It was shown that the sharp peak in the E2g Raman spectrum of superconducting MgB2 was due to a bound state caused by the electron-phonon coupling. The theory explained why this peak appeared only in the spectra with E2g symmetry and only in the σ and not the π bands. The properties of the bound state and the Raman spectrum were also investigated in the presence of impurity scattering.

Raman Scattering from a Superconductivity-Induced Bound State in MgB2. R.Zeyher: Physical Review Letters, 2003, 90[10], 107002 (3pp)