Kohn anomaly in MgB2 by inelastic X-ray scattering -: art. no. 197004

We study phonons in MgB2 using inelastic x-ray scattering (1.6 and 6 meV resolution). We clearly observe the softening and broadening of the crucial E-2g mode through the Kohn anomaly along GammaM, in excellent agreement with ab initio calculations. Low temperature measurements ( just above and below T-c) show negligible changes for the momentum transfers investigated and no change in the E-2g mode at A between room temperature and 16 K. We report the presence of a longitudinal mode along GammaA near in energy to the E-2g mode that is not predicted by theory.