Umklapp scattering

Umklappprozess referred to in solid state physics, a scattering of phonons on the grid. Taking into account in the treatment of lattice vibrations deviations from the linear law of force between the lattice atoms, one obtains an interaction of phonons. The first anharmonic term describes the Dreiphononenprozesse. Dominated at a Dreiphononenprozess now out of the resulting wave vector of the first Brillouin zone, it is reduced by a reciprocal lattice vector. The lattice vector corresponding to this pulse is transmitted to the grid. It applies the quasi- momentum conservation.