Dispersion curves

A phonon is a collective motion of atoms or molecules in a crystal, a material in which atoms or molecules are periodically arranged. This kind of excitation of the crystal lattice can be either acoustic or optical and the associated wave can be either longitudinal or transverse. This wave is generally dispersive, i.e. its frequency depends on its wave number (the inverse of the wavelength). 
Phonons play a major role in many of the physical properties of condensed matter, such as thermal conductivity and electrical conductivity. The study of phonons is an important part of condensed matter physics.

Therefore a dispersion curve is a plot of frequency against wave. We show here one among the three acoustic phonons of a crystal. The animation illustrates the relation between the phonon wave, the associated lattice distortion and the dispersion curve.

Dispersion curves (html - 1.09 Ki)
Animation written in full javascript (my very first one !)
©2014 A.Filhol, ILL, Grenoble