what is 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. In other words, a phonon can be defined as a discrete unit of vibrational mechanical energy. 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. The concept of phonons was introduced in 1932 by Soviet physicist Igor Tamm, and the name phonon comes from the Greek word φωνή (phonē), which translates to sound or voice, because long-wavelength phonons give rise to sound. Phonons are analogous to photons, in fact, both possess almost identical properties. Both phonons and photons are bosons, meaning both particles have integral spins.