Microscopic origin of spin-orbital separation in Sr2CuO3

TL;DR

This paper explains the large orbiton dispersion observed in Sr2CuO3 by deriving a microscopic model, mapping it to a t-J model, and calculating the spectral function to match experimental RIXS results.

Contribution

The study provides a detailed microscopic derivation of the spin-orbital separation mechanism in Sr2CuO3 and connects it to observable RIXS spectra.

Findings

Derived a microscopic spin-orbital superexchange model.

Mapped orbiton motion to a single hole in a t-J model.

Calculated orbiton spectral function matching RIXS data.

Abstract

Recently performed resonant inelastic x-ray scattering experiment (RIXS) at the copper L3 edge in the quasi-1D Mott insulator Sr2CuO3 has revealed a significant dispersion of a single orbital excitation (orbiton). This large and unexpected orbiton dispersion has been explained using the concept of spin-orbital fractionalization in which orbiton, which is intrinsically coupled to the spinon in this material, liberates itself from the spinon due to the strictly 1D nature of its motion. Here we investigate this mechanism in detail by: (i) deriving the microscopic spin-orbital superexchange model from the charge transfer model for the CuO3 chains in Sr2CuO3, (ii) mapping the orbiton motion in the obtained spin-orbital model into a problem of a single hole moving in an effective half-filled antiferromagnetic chain t-J model, and (iii) solving the latter model using the exact diagonalization and obtaining the orbiton spectral function. Finally, the RIXS cross section is calculated based on the obtained orbiton spectral function and compared with the RIXS experiment.