Metal-insulator transition and electronic structure in Pr-doped Bi2Sr2(Caz, Pr1-z)Cu2O8+y

Substitution of Ca for Pr in Bi2Sr2(Caz, Pr1-z)Cu2O8+y leads to an insulator-metal transition at a critical concentration zc=0.52. The partial Pr-4f density of states of the insulating sample (z=0.4) was extracted utilizing the Pr 4d-4f Super-Coster-Kronig resonance in the resonant photoemission. The 4f-emission consists of a single peak at 1.36 eV binding energy and shows a strongly asymmetric Doniach-Sunjic line shape. This indicates an electronic band continuum with a sharp cutoff at EF even in the insulating sample. This finding excludes a band gap at EF in the insulator, but supports the existence of localized states at EF due to disorder. (orig.)