Theory Meets Experiment in Low-Dimensional Structures with Correlated Electrons

Two-particle (2P) excitations provide the prime path to probe and to manipulate electronic states of materials. Examples include optical experiments, electron loss spectroscopy, inelastic x-ray or neutron scattering. Theoretical description of 2P excitations in correlated materials is notoriously difficult as these involve unbound electron-hole pairs as well as bound pairs such as spin waves or excitons. The behavior of 2P excitations is particularly interesting in states with spontaneously broken symmetry where gapless collective modes are predicted by symmetry considerations. I will present dynamical mean-field calculation of collective modes in excitonic magnets at intermediate and weak coupling to demonstrate capability of this approach. As a material specific example, I will present simulation of RIXS spectra of LaCoO₃ where spinful excitons where recently observed.