Resonant Inelastic X-Ray Scattering inNd2CuO4

We report inelastic x-ray scattering studies of charge excitations in insulating ${\mathrm{Nd}}_2{\mathrm{CuO}}_4$ as a function of incident photon energy. An excitation of $\sim 6\mathrm{eV}$ is observed when the incident photon energy is tuned through the Cu $K$ edge. This is interpreted as resonantly enhanced inelastic x-ray scattering. Numerical calculations identify the 6 eV feature as a charge-transfer excitation to the antibonding state and suggest that nonlocal effects play a role in determining the shape of the resonance.