title: Spin-exchange dynamical structure factor of the S=1/2 Heisenberg chain.
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.
authors.affiliation: Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
authors.forename: Antoine
authors.initials: A
authors.lastname: Klauser
authors.forename: Jorn
authors.initials: J
authors.lastname: Mossel
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Caux
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Brink