Dispersions of Many-Body Bethe strings

TL;DR

This study experimentally observes and characterizes the dispersion relations of Bethe string states in a one-dimensional quantum magnet, confirming theoretical predictions and highlighting their role in quantum spin dynamics.

Contribution

First direct experimental measurement of Bethe string dispersions in a 1D quantum magnet, validating Bethe Ansatz calculations and advancing understanding of many-body quantum states.

Findings

Observed Bethe string dispersions over the full Brillouin zone

Confirmed agreement between experimental data and Bethe Ansatz calculations

Identified magnetic field dependence of string state properties

Abstract

Complex bound states of magnetic excitations, known as Bethe string, were predicted almost a century ago to exist in one-dimensional quantum magnets 1. The dispersions of the string states have so far remained the subject of intensive theoretical studies 2-7. By performing neutron scattering experiments on the one-dimensional Heisenberg-Ising antiferromagnet SrCo2V2O8 in high longitudinal magnetic fields, we reveal in detail the dispersion relations of the string states over the full Brillouin zone, as well as their magnetic field dependences. Furthermore the characteristic energy, the scattering intensity and linewidth of the observed string states exhibit excellent agreement with our precise Bethe Ansatz calculations. Our results establish the important role of string states in the quantum spin dynamics of one-dimensional systems, and will invoke studies of their dynamical properties in more general many-body systems.