Electronic states of impurity atoms in noble-metal lattices

Abstract

Experimental Dingle-temperature anisotropies and impurity-induced Fermi-surface changes in nonmagnetic dilute alloys have been shown elsewhere to determine the Friedel phase shifts that characterize impurity scattering. In the present paper the Friedel phase shifts for various dilute alloys in noble-metal hosts are analyzed to yield the complex renormalization coefficients that describe the way in which backscattering modifies the wave-function amplitude on the impurity site, and the phase shifts that characterize potential scattering of conduction electrons at the Fermi level by the impurity. Our approach is based on an exact treatment of backscattering in a lattice of muffin-tin potentials. The influence of possible lattice distortion associated with alloying on the determination of impurity-state parameters is discussed. Impurity-state parameters are obtained for dilute noble-metal alloys which give information about the scattering potentials and, in some cases, charge shifts associated with alloying can be inferred. Various approximate treatments of backscattering are developed, which generally work well except in the vicinity of scattering resonances of the host or impurity atom.