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Abstract
The calculated properties of the charge perturbations around impurities in metals are summarized and contrasted with the experimental situation in this field.
The effects of coupling between the field gradient excited by the charge perturbation and the quadrupole moments of (host) nuclei on the nuclear magnetic resonance (N.M.R.) signal are summarized and various kinds of experiment based on this quadrupole effect are discussed.
The gross overall features of the charge perturbation are established by analysing N.M.R. data for copper and aluminium based alloys. This analysis leads to the conclusion that simple theories can account for the main experimental findings, but details, in particular the anisotropy of the charge perturbation, cannot be fully explained because band structure effects play an important role.
The relevance of phase-shift analysis is also assessed, and its applicability in cases of complicated Fermi surfaces is discussed. Effects connected with the energy dependence of the scattering potentials for three-dimensional transition metal impurities are reviewed and evidence for the depression of the charge perturbation near to the impurities is summarized for copper and aluminium based alloys. Temperature dependence, caused by the thermal smearing of the host Fermi surface, by the reduction of the mean free path and by the temperature dependence of the scattering potential (connected to the Kondo effect) is also discussed.
Other relevant experimental techniques are briefly summarized together with effects determined by the charge perturbation around the impurities.