Charge ordering in ladder vanadate NaV₂O₅ evidenced by core-level photoemission

Core-level X-ray photoelectron spectrum of the ladder vanadate NaV₂O₅ is calculated with an extended Hubbard model, adopting a numerically exact diagonalization method based on the Lanczos algorithm. The result shows that the d band filling dependence of the spectrum deviates considerably from the simple statistical ratio of V⁴⁺ to V⁵⁺ in NaV₂O₅, which indicates the importance of the delocalized nature of d electron states. It is also shown that the spectrum is significantly influenced by the intersite Coulomb interaction and lattice distortion, which are responsible for the charge ordering.