Electron Correlation Effects in Resonant Inelastic X-ray Scattering of   NaV2O5
  Element- and site-specific resonant inelastic x-ray scattering spectroscopy (RIXS) is employed to investigate electron correlation effects in {$\rm NaV_2O_5$}. 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 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 $U= 3.0 \pm 0.2$ eV. 
G. P. Zhang (1,2), T. A. Callcott (1), G. T. Woods (1), L. Lin (1),   Brian Sales (3), D. Mandrus (3), and J. He (3) ((1)U.o...