Bimagnon studies in cuprates with Resonant Inelastic X-ray Scattering at the O K edge. I - An assessment on La2CuO4 and a comparison with the excitation at Cu L3 and Cu K edges

TL;DR

This study demonstrates that O K edge RIXS effectively probes bimagnon excitations in La2CuO4, revealing distinct spectral features compared to Cu L3 and K edges, thus offering unique insights into magnetic excitations in cuprates.

Contribution

It provides the first comprehensive assessment of O K edge RIXS for bimagnon detection in cuprates, highlighting its unique spectral fingerprints and comparing it with other edges.

Findings

O K edge RIXS shows a dominant peak at 450 meV with minimal dispersion.

Differences in bimagnon spectra between O K and Cu edges are explained by sampling of the bimagnon continuum.

O K RIXS offers unique insights into magnetic excitations near the Brillouin zone center.

Abstract

We assess the capabilities of magnetic Resonant Inelastic X-ray Scattering (RIXS) at the O $K$ edge in undoped cuprates by taking La_{2}CuO_{4} as a benchmark case, based on a series of RIXS measurements that we present here. By combining the experimental results with basic theory we point out the fingerprints of bimagnon in the O $K$ edge RIXS spectra. These are a dominant peak around 450 meV, the almost complete absence of dispersion both with $\pi$ and $\sigma$ polarization and the almost constant intensity vs. the transferred momentum with $\sigma$ polarization. This behavior is quite different from Cu $L_3$ edge RIXS giving a strongly dispersing bimagnon tending to zero at the center of the Brillouin zone. This is clearly shown by RIXS measurements at the Cu $L_3$ edge that we present. The Cu $L_3$ bimagnon spectra and those at Cu $K$ edge - both from the literature and from our data - however, have the same shape. These similarities and differences are understood in terms of different sampling of the bimagnon continuum. This panorama points out the unique possibilities offered by O $K$ RIXS in the study of magnetic excitations in cuprates near the center of the BZ.