Electron Correlation in Ta 5d band of Ta2NiSe5 Deduced from Ta 4f Core-Level Photoemission Analysis

Core-level photoemission spectra of Ta2NiSe5 are theoretically analyzed on the basis of numerically-exact diagonalization calculations applied for the extended attractive Hubbard model in one dimension. The attractive intersite interaction (V) mimics the effective attraction between Ta 5d electrons caused by the excitonic coupling. The asymmetric line shape of the Ta 4f photoemission spectrum clearly indicates the existence of an appreciable number of correlated Ta 5d electrons, which is consistent with the semi-metal-like band structure below the structural phase transition temperature (= 328 K). The ground state may be located close to the boundary between SDW and superconductivity in the phase diagram of the extended attractive Hubbard model. The theoretical analysis is also applied to the Ni 2p photoemission.