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Introduction to Phonons
Phonons are quanta of vibrational energy in a lattice.
This can be transverse, longitudinal, or a mixture.
There are two main types of phonon - optical and acoustic. In acoustic phonons displacement from lattice equilibrium for all particles is like a cosine function.
Optical phonons require at least two types of atom in the lattice. The two atoms behave slightly differently to the vibration, and the effect is like two overlapping cosine functions.
There are two main types of phonon - optical and acoustic. In acoustic phonons displacement from lattice equilibrium for all particles is like a cosine function.
Optical phonons require at least two types of atom in the lattice. The two atoms behave slightly differently to the vibration, and the effect is like two overlapping cosine functions.
Schematic example: Optical and acoustic phonons
Frequency ~1012-1013 Hz (Infra red
active)
In optical phonons, the two distinct particles move in
opposite directions
In acoustic phonons, the wave is more simple.
Transverse
Frequency ~103-1014 Hz (Not IR active)
Single phonon simulator animation: Click in the green box
to give a 2d phonon wavevector, k
Red line follows dispacement of one ion
Optical
Transverse
Lattice spacing