Kohn effect and the Fermi surface in copper studied by neutron spectroscopy

The Kohn effect in copper has been investigated at 80 K for selected regions of the phonon dispersion curves, where the effect was believed to be relatively strong, and where good instrumental resolution is obtainable for the neutron spectrometer used. Kohn anomalies are weak in copper, but they can be observed if the measurements are made with due care. About twenty anomalies have been studied and analyzed with the aid of an eighth-nearest-neighbor Born-von K\'arm\'an model. The anomalies are interpreted in terms of points on the Fermi surface in the (100) and (110) planes. The representation picture of the Fermi surface thus obtained is in good agreement with those derived from the Haas-van Alphen and magnetoacoustical measurements.