Phonon anomalies in transition-metal nitrides: TiN

For the first time we have observed soft-mode behavior in a superconducting transition-metal nitride. The phonon dispersion curves measured by inelastic neutron scattering exhibit sharp minima for the longitudinal-acoustic branches in the high-symmetry directions. The experimental results are well reproduced by calculations based on a double-shell model. The dispersion curves of TiN are similar to those of NbC except for significant difference in the anomalous region.