New analysis of the electronic excitations in the Mott insulator Nd$_2$CuO$_4$ using momentum-dependent intensity maps

Resonant inelastic X-ray scattering (RIXS) is a rapidly advancing technique that allows the measurement of electronic excitations in correlated-electron systems. In order to extend this technique, we developed a new circle to perform azimuthal rotations of the crystal. This allowed us to perform precise measurements of the electronic excitations as a function of the momentum transfer in the copper-oxygen planes and the incident photon polarization. As a result, we discovered that Cu K edge RIXS is at most weakly polarization dependent when the polarization is kept in the copper-oxygen planes. We used this new circle to determine the intensity variations of different energy-loss excitations across many Brillouin zones. These intensity maps as well as inelastic spectra measured at high-symmetry points in the Brillouin zone allow an improved analysis of the electronic-excitation spectral weight in this material. We discuss our findings in the context of past measurements on other cuprate systems.