d-d excitations and charge ordering in La5/3Sr1/3NiO4

We report the temperature dependence of the crystal-field-excitation spectrum in La5/3Sr1/3NiO4 by resonant inelastic x-ray scattering at the Ni K edge. Two distinct excitations are observed in the 1-3 eV energy range, in agreement with optical conductivity studies. The temperature dependence of the low-energy spectral weight is found to be closely related to the appearance and suppression of charge ordering. The relation between these crystal-field excitations and the stripe ordering is discussed.