Charge-density-wave phase elasticity of the blue bronze

We report neutron inelastic scattering measurements of the dispersion of the phase mode of the charge-density-wave (CDW) collective excitations in the blue bronze. Anisotropy and temperature-dependence analysis yields phase elasticity parameters relevant for a classical deformable model of CDW. The considerable stiffening of the longitudinal phason velocity observed upon cooling clearly shows that Coulomb forces play a fundamental role in CDW deformation processes.