Breakdown of Linear Spin-wave Theory and Existence of Spinon Bound States in the Frustrated Kagome Lattice Antiferromagnet

TL;DR

This study investigates the spin dynamics of a kagome lattice antiferromagnet, revealing limitations of linear spin-wave theory and evidence for spinon bound states through neutron scattering experiments.

Contribution

It demonstrates the breakdown of linear spin-wave theory in describing certain modes and provides evidence for spinon bound states in the frustrated kagome lattice.

Findings

Linear spin-wave theory describes flat and magnon modes well.

Identification of weakly dispersive modes as two-spinon bound states.

Observation of continuum scattering at high temperature.

Abstract

Spin dynamics of the spin-1/2 kagome lattice antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$ was studied using high-resolution, time-of-flight inelastic neutron scattering. The flat mode, a characteristic of the frustrated kagome antiferromagnet, and the low-energy dispersive mode, which is dominated by magnons, can be well described by the linear spin-wave theory. However, the theory fails to describe three weakly dispersive modes between 9 and 14 meV. These modes could be attributed to two-spinon bound states, which decay into free spinons away from the zone center and at a high temperature, giving rise to continuum scattering.