Phason Dynamics of Incommensurate Crystals

Abstract

It is shown that phase modulations (phasons) of the order parameters of incommensurate lattices are always diffusive at sufficiently large wavelengths $\ensuremath{\lambda}$. In general there is a crossover from diffusive behavior for $\ensuremath{\lambda}\ensuremath{\gg}\ensuremath{\Lambda}$ to propagating behavior for $\ensuremath{\lambda}\ensuremath{\ll}\ensuremath{\Lambda}$ where $\ensuremath{\Lambda}$ is a mean free path due to nonlinear interactions. The present results explain why light- and neutron-scattering experiments probe different dynamical behavior of phasons.