what is a phonon

A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. It is a type of quasiparticle, and the quantum mechanical description of an elementary vibrational motion in which a lattice of atoms or molecules uniformly oscillates at a single frequency. Phonons are analogous to photons, and like photons, they are bosons and not conserved; they can be created or destroyed in collisions. The energy of each phonon is given by E = ħω, where ω is the angular frequency and ħ is the reduced Planck’s constant. Phonons 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. In a crystal, the atoms are neatly arranged in a uniform, repeating structure; when heated, the atoms can oscillate at specific frequencies, and the bonds between the individual atoms in a crystal behave essentially like springs.