Low-energy excitonic resonances in metals. II. Cluster calculations for divalent impurities in Li metal

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Abstract
Recent spectroscopic studies of dilute and concentrated divalent impurities in alkali metals identify an important new type of local-excitation phenomenon. The results are not consistent with simple band-theory models for alloys. Instead they suggest that locally excited configurations of impurities occur in the metallic host. These local excitations are resonant with the band-to-band continuum of the host, and their excitation energies are significantly red-shifted from those of the free atom. Chemically similar impurities absorb light at approximately the same frequency in a given host. These local excitations seem to persist in the perfect divalent metal as well. A variety of line shapes apparently derived from Fano-like interference between the local excitation and the host conduction band is observed. We describe a theory of these phenomena based upon cluster calculations, including many-body corrections.