MULTISITE EFFECTS ON THE CORE-LEVEL PHOTOEMISSION IN Sr2RuO4

Multi-Ru-site effects on the photoemission from the Ru 3d core level in Sr 2 RuO 4 are discussed on the basis of numerical diagonalization calculations for large-size cluster models. It is shown that the electrons on the Ru 4d ions neighboring the core-hole site participate actively in the core-hole screening, which indicates the importance of so-called "nonlocal screening" in Sr 2 RuO 4. However, since it occurs via the Ru 4d(xy)– O 2pπ bonding, the photoemission intensity which corresponds to the nonlocal screening is not large, compared with the Cu 2p photoemission in high-Tc-related cuprates. From the spectral analysis, the Coulomb interaction strength between Ru 4d electrons is estimated to be comparable with the width of Ru dε bands. In other words, Sr 2 RuO 4 belongs to a category of strongly correlated electron systems.