The Spin-Exchange Dynamical Structure Factor of the S=1/2 Heisenberg Chain

TL;DR

This paper calculates the spin-exchange dynamical structure factor of the S=1/2 Heisenberg chain as measured by RIXS, revealing fractionalization into spinon states and highlighting the spectral weight distribution beyond low-energy theories.

Contribution

It provides a detailed theoretical analysis of the RIXS response in the Heisenberg chain, emphasizing the fractionalization into spinons and the spectral weight distribution at higher energies.

Findings

Two-spin RIXS excitations fractionalize into two spinon states.

RIXS spectral weight is dominated by higher-energy excitations.

The continuum lower bound matches that of neutron scattering, despite different symmetry sectors.

Abstract

We determine the spin-exchange dynamical structure factor of the Heisenberg spin chain, as is measured by indirect Resonant Inelastic X-ray Scattering (RIXS). We find that two-spin RIXS excitations nearly entirely fractionalize into *two spinon* states. These share the same continuum lower bound as single-spin neutron scattering excitations, even if the relevant final states belong to orthogonal symmetry sectors. The RIXS spectral weight is mainly carried by higher-energy excitations, and is beyond the reach of the low-energy effective theories of Luttinger liquid type.