Question: Localized vibrations in a crystal can be represented by a superposition of phonon modes with different wavevectors. Show that the centre of gravity of

Localized vibrations in a crystal can be represented by a superposition of

Localized vibrations in a crystal can be represented by a superposition of phonon modes with different wavevectors. Show that the centre of gravity of such a wave packet moves with the group velocity Vg dw dk

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