Editing Phonon (section)

===Lattice waves===
[[File:Lattice wave.svg|class=skin-invert-image|200px|thumb|right|Phonon propagating through a square lattice (atom displacements greatly exaggerated)]]
Due to the connections between atoms, the displacement of one or more atoms from their equilibrium positions gives rise to a set of vibration [[wave]]s propagating through the lattice. One such wave is shown in the figure to the right. The [[amplitude]] of the wave is given by the displacements of the atoms from their equilibrium positions. The [[wavelength]] ''λ'' is marked.

There is a minimum possible wavelength, given by twice the equilibrium separation ''a'' between atoms. Any wavelength shorter than this can be mapped onto a wavelength longer than 2''a'', due to the periodicity of the lattice. This can be thought of as a consequence of the [[Nyquist–Shannon sampling theorem]], the lattice points being viewed as the "sampling points" of a continuous wave.

Not every possible lattice vibration has a well-defined wavelength and frequency. However, the [[normal mode]]s do possess well-defined wavelengths and [[frequency|frequencies]].