Flip process

Folding process in the square grid: wave vectors emerging from the 1st Brillouin zone are reduced by one grid vector

In solid-state physics, the folding process refers to the scattering of phonons on the lattice . If one takes into account deviations from the linear force law between the lattice atoms when treating the lattice vibrations, then one obtains an interaction of the phonons. The first anharmonic term describes the three-phonon processes. If the resulting wave vector protrudes from the first Brillouin zone in a three-phonon process , it is reduced by a reciprocal lattice vector . The impulse corresponding to this grid vector is transmitted to the grid. So the quasi-momentum conservation applies . ${\displaystyle k+k'}$ ${\displaystyle G}$ ${\displaystyle G}$ ${\displaystyle \hbar G}$ ${\displaystyle \hbar k+\hbar k'=\hbar k''+\hbar G}$

It was first described by Rudolf Peierls .

literature

• Neil W. Ashcroft, N. David Mermin: Solid State Physics . Saunders College Publishing, New York 1976, ISBN 0-03-083993-9 , pp. 501-505, 526-528 .
• Konrad Kopitzki, Peter Herzog: Introduction to Solid State Physics . BG Teubner, Bonn 1986, ISBN 3-8351-0144-7 , p. 96 ff .