Multisite effects on the core-level photoemission in Sr₂RuO₄

Multi-Ru-site effects on the photoemission from the Ru3d core level in Sr2RuO4 are discussed on the basis of numerical diagonalization calculations for large-size cluster models. It is shown that the electrons on the Ru4d ions neighboring the core-hole site participate actively in the core-hole screening, which indicates the importance of so-called "nonlocal screening" in Sr₂RuO₄. However, since it occurs via the Ru4d(xy)-O2pπ bonding, the photoemission intensity which corresponds to the nonlocal screening is not large, compared with the Cu2p photoemission in high-T_c-related cuprates. From the spectral analysis, the Coulomb interaction strength between Ru4d electrons is estimated to be comparable with the width of Rudε bands. In other words, Sr₂RuO₄ belongs to a category of strongly correlated electron systems.