# Theoretical study of the spin and charge dynamics of two-leg ladders as probed by resonant inelastic x-ray scattering

## TL;DR

This paper provides a comprehensive theoretical analysis of RIXS spectra in two-leg cuprate spin-ladders, revealing various exotic spin and charge excitations across different doping and coupling regimes.

## Contribution

It offers new insights into the spin and charge dynamics in cuprate ladders by identifying specific excitations in RIXS spectra, including bound states and confined spinons, in both undoped and doped cases.

## Key findings

- Identification of one-triplon and triplet two-triplon excitations in undoped ladders.
- Observation of a bound charge and spin quasiparticle in doped ladders.
- Discovery of bound singlet two-triplon excitations and confined spinons.

## Abstract

Resonant inelastic x-ray scattering (RIXS) has become an important tool for studying elementary excitations in correlated materials. Here, we present a systematic theoretical investigation of the Cu L-edge RIXS spectra of undoped and doped cuprate two-leg spin-ladders in both the non-spin-conserving (NSC) and spin-conserving (SC) channels. The spectra are rich and host many exotic excitations. In the NSC-channel of the undoped case, we identify one-triplon and bound $\textit{triplet}$ two-triplon excitations in the strong-rung coupling limit, as well as confined spinons in the weak-rung coupling limit. In the doped case, we observe a quasiparticle excitation formed from a bound charge and spin-$\frac{1}{2}$ in the strong-rung coupling limit. In the SC-channel, we also identify several new features, including bound $\textit{singlet}$ two-triplon excitations and confined spinons in the undoped ladders in the strong- and weak-rung coupling limits, respectively. Conversely, in the doped case, the SC channel primarily probes both gapless and gapped charge excitations. Finally, we revisit the available data for the ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ in the context of our results.