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M Quack
M Quack is offline
#2
Mar16-12, 09:28 AM
P: 640
It is the phonon energy (or frequency) as function of the wave vector (i.e. wavelength and direction of propagation) . For each wave vector there are several "branches" of phonons, i.e. modes with different energies. One distinguishes between "acoustic" phonons with E=0 at k=0 and optical phonons with E>0 at k=0.