Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds

TL;DR

This study uses high-resolution RIXS to analyze the complex spin excitations in cuprate parent compounds, revealing multiple-magnon features and their agreement with neutron scattering, advancing understanding of quantum magnetism.

Contribution

It demonstrates that RIXS can effectively probe the rich and complex spin spectra of cuprates, including higher-order magnon excitations and bimagnon features.

Findings

Single-magnon dispersion matches neutron data

Asymmetric lineshape suggests higher-order effects

Bimagnon feature coincides with optical spectroscopy results

Abstract

Thanks to high resolution and polarization analysis, resonant inelastic x-ray scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a rich set of properties of the spin 1/2 antiferromagnetic square lattice of cuprates. The leading single-magnon peak energy dispersion is in excellent agreement with the corresponding inelastic neutron scattering measurements. However, the RIXS data unveil an asymmetric lineshape possibly due to odd higher order terms. Moreover, a sharp bimagnon feature emerges from the continuum at (1/2,0), coincident in energy with the bimagnon peak detected in optical spectroscopy. These findings show that the inherently complex spin spectra of cuprates, an exquisite manifestation of quantum magnetism, can be effectively explored by exploiting the richness of RIXS cross sections.