Electron Correlation Effects in Resonant Inelastic X-Ray Scattering ofNaV2O5

Element- and site-specific resonant inelastic x-ray scattering spectroscopy (RIXS) is employed to investigate electron correlation effects in ${\mathrm{NaV}}_2{\mathrm{O}}_5$. In contrast to single photon techniques, RIXS at the vanadium $L_3$ edge is able to probe $d-d^{*}$ transitions between V $d$-bands. A sharp energy loss feature is observed at $-1.56\mathrm{}\mathrm{eV}$, which is well reproduced by a model calculation including correlation effects. The calculation identifies the loss feature as excitation between the lower and upper Hubbard bands and permits an accurate determination of the Hubbard interaction term $U=3.0\mathrm{}\pm 0.2\mathrm{eV}$.