Ru 3d core-level x-ray photoemission spectra of various ruthenates areexamined. They show in general two-peak structures, which can be assigned asthe screened and unscreened peaks. The screened peak is absent in a Mottinsulator, but develops into a main peak in the metallic regime. This spectralbehavior is well explained by the dynamical mean-field theory calculation forthe single-band Hubbard model with on-site core-hole potential using the exactdiagonalization method. The new mechanism of the core-level photoemissionsatellite can be utilized to reveal the Mott transition phenomenon in variousstrongly correlated electron systems, especially in nano-scale devices andphase-separated materials.
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