Kohn anomaly
The Kohn anomaly (after Walter Kohn , who discovered it in 1959) is an anomaly of the dispersion relation of phonons . It is a logarithmic divergence in the derivation of the dispersion relation. This divergence comes from the interaction between phonons and electrons and always occurs on the Fermi surface , so that information about the Fermi surface can also be obtained by measuring the dispersion.
The Kohn anomaly is u. a. responsible for the Peierls transition in one-dimensional molecule chains such as polyethine and the Jahn-Teller transition in three-dimensional crystals . It can cause a spontaneous break in the lattice symmetry due to electronic energy minimization.
It was first demonstrated experimentally in 1961 in the group of Bertram Brockhouse in Chalk River.
Individual evidence
- ^ W. Kohn: Image of the Fermi Surface in the Vibration Spectrum of a Metal . In: Physical Review Letters . tape 2 , no. 9 May 1959, p. 393-394 , doi : 10.1103 / PhysRevLett.2.393 .
- ↑ Brockhouse, KR Rao., ADB Woods, Phys. Rev. Lett., Vol. 7, 1961, p. 93, Brockhouse et al. a. Phys. Rev., Volume 128, 1962, p. 93