Inelastic neutron scattering measurements were made of the phonon density of states in Mg11B2, which had a superconducting transition at 39.2K. The acoustic phonons extended in energy to 36meV, and there were highly dispersive optical branches peaking at 54, 78, 89 and 97meV. A simple Born-von Karman model reproduced the mode energies, and provided an estimate of the electron-phonon coupling of λ which was about 0.9. The estimated B and Mg contributions to the isotope effect were in qualitative agreement with experiment. The data confirmed that a conventional phonon mechanism, with moderately strong electron-phonon coupling, could explain the observed superconductivity.

Phonon Density of States in MgB2. R.Osborn, E.A.Goremychkin, A.I.Kolesnikov, D.G.Hinks: Physical Review Letters, 2001, 87[1], 017005 (3pp)