The S=1/2 chain in a staggered field: High-energy bound-spinon state and the effects of a discrete lattice

TL;DR

This study combines experimental neutron scattering and theoretical modeling to reveal a high-energy bound-spinon state in a staggered field S=1/2 chain, highlighting lattice effects and spinon confinement.

Contribution

It presents the first observation of a high-energy bound-spinon state in a real material and develops a mean-field theory incorporating lattice effects to explain it.

Findings

Observation of a novel high-energy bound-spinon state

Mean-field theory explains the state and lattice effects

Excellent agreement between theory and neutron scattering data

Abstract

We report an experimental and theoretical study of the antiferromagnetic S=1/2 chain subject to uniform and staggered fields. Using inelastic neutron scattering, we observe a novel bound-spinon state at high energies in the linear chain compound CuCl2 * 2((CD3)2SO). The excitation is explained with a mean-field theory of interacting S=1/2 fermions and arises from the opening of a gap at the Fermi surface due to confining spinon interactions. The mean-field model also describes the wave-vector dependence of the bound-spinon states, particularly in regions where effects of the discrete lattice are important. We calculate the dynamic structure factor using exact diagonalization of finite length chains, obtaining excellent agreement with the experiments.