High-order van Hove singularity in the magnon excitations of SrCuO2

The van Hove singularity (VHS) is an important ingredient in the rich physics of two-dimensional electronic systems. Recently, high-order VHS has been reported in electronic twisted bilayer graphene and kagome metals, but the link between higher-order divergent DOS and electronic instabilities has not been established yet. Our recent medium resolution RIXS study shows that the magnon excitation of SrCuO2 displays characteristic resembling a high-order VHS. Our analysis further reveals enhanced quantum fluctuations that possibly result from the stronger singularity. However, the limit of energy resolution and the accessible range of reciprocal space preclude an unambiguous conclusion. Here, we propose to clarify the nature of the magnon VHS in SrCuO2 by exploring its out-of-plane dispersions using ultrahigh-resolution Cu L-edge RIXS. The realization of high-order magnon VHS will provide a new perspective in understanding the magnetism of cuprate superconductors.