Fig. 3.

An illustration of various spin excitations through elementary spin-flips. a The ΔS_tot=1 direct spin-flip process that can occur in an inelastic neutron scattering experiment, which primarily decays into two-spinon excitations that are visualized as domain walls in the antiferromagnetic (AFM) background⁵. b The same ΔS_tot=1 spin-flip process in RIXS, which is accessible in materials with strong spin–orbit coupling in the core level³². c The indirect double spin-flip process at the oxygen K-edge, which occurs via the multi-orbital hopping processes sketched in Fig. 1e. This process generates a nearest-neighbour double spin flip, which predominantly decays into a two-spinon excitation^22,38. d A second-order process at the oxygen K-edge that produces four-spinon excitations. Here, the absence of the spin in the AFM chain allows double spin-flips to occur on the sites adjacent to the missing spin. These double spin-flips generate spinon excitations away from the site where the core hole is created. The subsequent decay of the core hole then produces two additional spinons in its vicinity. This process requires a long-lived core-hole to allow for sufficient time to generate the two double spin-flips before the core-hole decay occurs