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A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids.A type of quasiparticle in physics, [1] a phonon is an excited state in the quantum mechanical quantization of the modes of vibrations for elastic structures of interacting particles.
If the vibration occurs lengthwise in the direction of the wave and involves contraction and relaxation of the lattice, the phonon is called a "longitudinal phonon". Alternatively, the atoms may vibrate side-to-side, perpendicular to wave propagation direction; this is known as a "transverse phonon”.
In fluids, the phonon is longitudinal and it is the Goldstone boson of the spontaneously broken Galilean symmetry.In solids, the situation is more complicated; the Goldstone bosons are the longitudinal and transverse phonons and they happen to be the Goldstone bosons of spontaneously broken Galilean, translational, and rotational symmetry with no simple one-to-one correspondence between the ...
The phonon, which is either generated or annihilated, has a wavevector which is a linear combination of the incident and scattered wavevectors. This orientation will become more apparent and important when the orientation of the experimental setup is discussed. Geometric relationships between longitudinal, L, and transverse, T, acoustic waves.
These scattering mechanisms are: Umklapp phonon-phonon scattering, phonon-impurity scattering, phonon-electron scattering, and phonon-boundary scattering. Each scattering mechanism can be characterised by a relaxation rate 1/ τ {\displaystyle \tau } which is the inverse of the corresponding relaxation time.
Slack phonon conductivity model mainly considering acoustic phonon scattering (three-phonon interaction) is given as [27] [28] =, = /, / (>,, where M is the mean atomic weight of the atoms in the primitive cell, V a =1/n is the average volume per atom, T D,∞ is the high-temperature Debye temperature, T is the temperature, N o is the number of ...
Here, the + corresponds to phonon emission and – for phonon absorption during the scattering event. A note, because q ⊥ u ( r , t ) {\displaystyle q\perp u(r,t)} for transverse phonons, only interactions with longitudinal phonons are non-zero.
For systems with many phonon branches, the relation does not necessarily hold, as the permittivity for any pair of longitudinal and transverse modes will be altered by the other modes in the system. The Lyddane–Sachs–Teller relation is named after the physicists R. H. Lyddane, Robert G. Sachs, and Edward Teller. Phonon band structure in ...