Phonon

A phonon is a quasiparticle of vibrational energy that uniformly oscillates at a single frequency in a medium. They can be thought of as quantized sound waves, similar to the way photons are quantized light waves, but unlike photons, phonons are vibrations in a lattice of atoms. Phonons have both wave and particle-like properties, in a way related to the wave–particle duality of quantum mechanics.

The study of phonons is an important part of condensed matter physics. They play a major role in many of the physical properties of condensed matter systems, such as thermal conductivity and electrical conductivity, as well as in models of neutron scattering and related effects.

A type of quasiparticle in physics, a phonon is an excited state in the modes of vibrations of an elastic structure. In solids with more than one atom in the smallest unit cell, phonons exhibit both acoustic and optical qualities. In the context of optically trapped objects, the quantized vibration mode can be defined as phonons as long as the modal wavelength of the oscillation is smaller than the size of the object.