Temperature dependent phonon dispersion in 2H-NbSe2 investigated using inelastic neutron scattering

The longitudinal low frequency acoustic and optic phonon modes of 2H-NbSe2 have been determined for the Gamma - M direction with inelastic neutron scattering at 50 K close to the charge density wave transition temperature. We found a softening of the two low frequency modes which are attributed to the same symmetry close to the charge density wavevector. We also found indications that the anomalous frequency seems to soften further for off-symmetry directions.