Theory of L-edge resonant inelastic x-ray scattering for magnetic excitations in two-leg spin ladder

TL;DR

This paper develops a theoretical framework for interpreting magnetic excitation spectra in two-leg spin ladder cuprates using RIXS, successfully explaining experimental observations and predicting how to detect specific excitations.

Contribution

The authors derive formulas for magnetic RIXS spectra in two-leg spin ladders, linking them to spin correlation functions, and demonstrate their application to experimental data.

Findings

The calculated RIXS spectrum matches the lower boundary of the two-triplon continuum.

Adjusting measurement geometry can reveal one-triplon dispersion around the zone center.

Weak high-energy intensity may be due to two-spin correlations detectable at the M3-edge.

Abstract

We study the magnetic excitation spectra of Cu L_{2,3}-edge resonant inelastic x-ray scattering (RIXS) from the spin-liquid ground state in two-leg spin ladder cuprates. Applying the projection method developed by the present authors, we have derived the formulas of the magnetic RIXS spectra, which are expressed by one- and two-spin correlation functions in the polarization changing and preserving channels, respectively. The one-spin correlation function includes both one- and two-triplon excitations and they are picked up separately by choosing rung wave vector -q_a=\pi and 0, respectively. An application to Sr_{14}Cu_{24}O_{41} reveals that the calculated RIXS spectrum captures well the dispersive behavior shown by the lower boundary of two-triplon continuum. By adjusting the geometrical configuration of the measurement, one-triplon dispersion around the zone center could be detectable in the RIXS experiment. The observed weak intensity in the higher energy region might be attributed to the two-spin correlation function, which could be detected more clearly at the M_{3}-edge RIXS spectra.