We investigate the multimagnon and the multispinon $L_3$-edge resonant inelastic x-ray scattering (RIXS) spectra of a spin-1/2 effective ${\tilde{J}}_1-{\tilde{J}}_2-{\tilde{J}}_3$ square lattice Heisenberg model in its Néel ordered phase. Motivated by the observation of satellite intensity peaks above the single magnon dispersion in the $L$-edge RIXS spectrum, we propose a resonating valence bond (RVB) inspired RIXS mechanism that incorporates the local site ultrashort core-hole lifetime (UCL) expansion. We compute the multimagnon and the multispinon excitations using $O(1/S)$ interacting spin-wave theory and Schwinger boson mean-field theory (SBMFT) formalism, respectively. We treat the x-ray scattering process up to second order in the UCL expansion. Our calculations of two-magnon, bimagnon, and three-magnon RIXS intensities reveal that interacting spin-wave theory fails to fully capture all the quantum correlations in the antiferromagnetic ordered phase. However utilizing the SBMFT framework, with a ground state that incorporates features of both the Néel order and fluctuating RVB components, we demonstrate that a RIXS bond-flipping mechanism provides an alternative deeper physical explanation of the satellite intensities. Specifically, we find that the spin-correlation spectra predicted by the fluctuating RVB mechanism aligns with higher-order UCL expansion results. We further show that the satellite intensity above the single-magnon mode can originate both from a one-to-three-magnon hybridization vertex process and from condensed spinons exhibiting Higgs mechanism. These features reflect the interplay of quantum fluctuation, entanglement, and gauge interaction effects of quantum magnetism probed by RIXS.

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• Antiferromagnetism
• Goldstone bosons
• Magnetization dynamics
• Magnons
• Spin dynamics
• Spinon