= Collective excitation
A <collective excitation> is a disturbance involving coordinated motion or a coordinated change of many microscopic constituents. It can behave as an effective mode with a well-defined <energy> and <momentum> even though no single constituent carries the whole pattern.
A <phonon> represents a quantized <lattice vibration>; a <magnon> represents a spin-wave excitation. Their dispersion and interactions encode material properties. The usefulness of the quasiparticle description depends on whether the excitation persists long enough to have a meaningful mode identity.
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