The structure factor for neutron scattering from a two-state system in metals

The authors consider the dynamics of a defect tunnelling between two trap sites in a metal. The interaction with conduction electrons is shown to influence strongly the defect motion at low temperatures. They calculate the structure factor for inelastic neutron scattering. The inelastic scattering peaks found at very low temperatures are shown to merge into a single quasi-elastic peak at higher temperatures. The width of the quasi-elastic peak narrows as the temperature is increased further. This behaviour results from the damping of the defect motion through the non-adiabatic response of the screening cloud. The present paper extends the authors previous results for symmetric two-state systems to the asymmetric case.