Momentum Dependence of Charge Excitations in the Electron-Doped SuperconductorNd1.85Ce0.15CuO4: A Resonant Inelastic X-Ray Scattering Study

Abstract

We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-$T_c$ superconductor ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_4$. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with $\mathbf{q}$-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.