Theoretical study of resonant inelastic X-ray scattering spectrum in nickelates

Tsutsui, Kenji; Toyama, Takami*; Koshibae, Wataru*; Maekawa, Sadamichi

The two-dimensional nickelate LaSrNiO has received special attention as a reference system of high- cuprates. The undoped nickelate (=0) has the charge-transfer gap in the optical conductivity. Upon doping of holes, a broad spectrum appears in the gap. We have shown theoretically that the broad spectrum comes from excitations to the low spin states. In the Ni -edge resonant inelastic X-ray scattering (RIXS) measurement, the momentum-resolved charge excitations are obtained. In this study, we examine theoretically the RIXS spectra on nickelates by using numerically exact diagonalization techniques on the two-band Hubbard model. We also calculate other spectra such as the dynamical charge density function and discuss what excitations appear in the RIXS spectrum.