Study of the origin of magnetic excitations at Γ-point in RIXS measurements on one-dimensional antiferromagnets*

We study the momentum-resolved resonant inelastic x-ray scattering (RIXS) cross-section at Cu L₃-edge of Sr₂CuO₃, a one-dimensional antiferromagnet. The RIXS cross-section at this edge consists of spin conserving (ΔS = 0) and spin non-conserving (ΔS = 1) channels for magnetic excitations. A recent work¹ has shown the existence of multi-spinons at the Γ-point in the ΔS = 0 channel. The exact nature of these excitations is still an open question due to the complicated RIXS cross-section. Using the ultrafast core-hole lifetime (UCL) expansion, we show that the higher order terms in UCL generate the excitations in the new phase and hence propose a new correlation function for studying these multi-spinons. Our work can open up a possibility to study the nature of these excitations in terms of spinons using Bethe ansatz. Additionally, we show that the scattering geometry can be used to resolve ΔS = 0 and ΔS = 1 components of the excitations in the RIXS spectra. 

[1] J. Schlappa, et. al., (2018), arXiv:1802.09329.