Band-like/atomic-like duality of dd excitations in cuprates

The fascinating properties of high Tc superconducting cuprates are often attributed to the peculiar entwining of sev-eral degrees of freedom (charge density and anisotropy, spin, lattice modes). This implies that the corresponding excitations all have comparable energies, lying in the mid (<500 meV) and far infrared range (<100 meV), and are often of mixed character. Aside to the low energy region, RIXS spectra are dominated by the dd excitations, which are often dismissed as uninteresting. However, two recent experiments are now hinting to band-like effects occurring in the dd excitations of cuprates. We propose to measure the azimuthal (φ) dependence of the dd excitations in the striped cuprate LSCO, at different doping levels, to confirm the existence of unexpected jumps in the dd intensi-ty. The doping, temperature and q dependence of these discontinuities will confirm if this effect is band-like, possi-bly telling us which low energy order is involved in this phenomenology.