Theory of Multi-band Indirect K-edge Bimagnon Resonant Inelastic X-ray Scattering Spectrum

Magnetic correlations can give rise to two electron spin-flip (bimagnon) excitations in a quantum Heisenberg magnet. In recent years Resonant Inelastic X-ray Scattering (RIXS) has emerged as a powerful spectroscopic technique to study elementary excitations, including bimagnon processes, across the entire Brillouin zone in strongly correlated materials. Utilizing linear spin wave theory, I will describe our research effort to compare and contrast the results of the RIXS response of a bicollinear antiferromagnet (α-FeTe) and the block collinear antiferromagnet (K₂Fe₄Se₅) system, respectively. We will highlight the various features of the intraband and interband RIXS scattering channels, including the presence or absence of multi-peak structures. The number of peaks provide a clue on the various bimagnon excitation processes that can be supported both in and within the acoustic and optical magnon branches present in the material.