Resolving the nature of electronic excitations in resonant inelastic X-ray scattering

Resonant inelastic X-ray scattering (RIXS) has recently risen to becoming a versatile probe of elementary bosonic excitations in strongly correlated electron systems. However, various excitations with different charge, spin, and orbital nature are widely entangled in RIXS spectral axis, often complicating its interpretation. Here, we demonstrate a systematic method for the extraction of the character of excitations as imprinted in the azimuthal dependence of the RIXS signal. Using this novel approach, we resolve the charge, spin, and orbital nature of elastic scattering, (para-)magnon/bimagnon modes, and higher energy dd excitations in magnetically-ordered and superconducting copper-oxide perovskites (Nd2CuO4 and YBa2Cu3O6.75). In particular, we use the characteristic tensorial nature of each excitation to precisely and reliably disentangle the charge and spin contributions to the low energy RIXS spectrum. This procedure enables to separately track the evolution of spin and charge spectral distributions in cuprates with doping. Our results demonstrate a new capability that can be integrated into the RIXS toolset, and that promises to be widely applicable to materials with intertwined spin, orbital, and charge excitations.