Phonon

A phonon is a quantized collective vibration of atoms in a solid, treated as a quasiparticle carrying vibrational energy and crystal momentum.

Lattice vibration: The collective oscillatory motion of atoms around their equilibrium positions in a crystal. Phonons are the quantized normal modes of these collective atomic motions.
Crystal lattice: A periodic arrangement of points representing the repeating structure of a crystalline solid. Its periodicity sets the allowed wavevectors and vibrational patterns for phonons.
Thermal conductivity: A material's ability to conduct heat in response to a temperature gradient. In many insulating crystals, phonons carry most of the heat.
Magnon: A quantized spin-wave excitation in a magnetically ordered material. Magnons quantize collective spin motion, whereas phonons quantize atomic displacement.
Normal mode: A pattern of oscillation in which a system's parts move at one frequency with fixed relative amplitudes and phases. Each allowed lattice normal mode can be quantized as a phonon.
Lattice dynamics: The theory of atomic motion and vibrational excitations in crystalline solids. Phonons are the quantum excitations described by lattice dynamics.
Specific heat capacity: The heat required to raise a unit mass or amount of a substance by one degree. The phonon spectrum determines how much vibrational energy a solid stores as temperature rises.
Photon: The quantum of the electromagnetic field, carrying energy and momentum. Unlike photons, phonons are quasiparticles tied to vibrations in a material.
Phonon dispersion: The relationship between a phonon's frequency and its wavevector in a material. It shows how phonon energies vary across the crystal's allowed vibrational modes.
Quantum harmonic oscillator: A quantum system with a quadratic potential and equally spaced energy levels. A lattice's independent vibrational modes behave as quantum harmonic oscillators.

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