Phonon density-of-states in the new superconductor MgB2

We provide here experimental data on the phonon density-of-states of MgB2 o btained by the inelastic neutron scattering technique. The measurements wer e performed for the natural boron-based magnesium diboride with use of a ti me-of-flight neutron spectrometer. Several phonon bands were observed in th e phonon spectrum at energies of about 33, 55, 82 and 99 meV. We show that the cut-off energy of the density-of-states occurs at around 105 meV which is much higher than expected so far from heat-capacity data and partially e xplains the high T-c value observed for MgB2. The characteristic phonon ene rgies are indicative of an intermediate coupling regime in this compound. W e conclude that a much needed neutron experiment aimed at the study of the isotopic effect in the phonon density-of-states of MgB2 is conceivable.