Spin dynamics of the $E_8$ particles

TL;DR

This study experimentally confirms the existence of $E_8$ particles in BaCo$_2$V$_2$O$_8$ through neutron scattering, analytical, and numerical methods, providing detailed insights into their energy spectra and dispersions.

Contribution

First direct experimental observation of $E_8$ particles in a quasi-1D antiferromagnet, combining neutron scattering with theoretical and numerical analysis.

Findings

Observation of $E_8$ excitations across the Brillouin zone

Matching experimental data with theoretical $E_8$ energy predictions

Clear dispersion measurements of the three lightest $E_8$ particles

Abstract

In this article, we report on inelastic neutron scattering measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under a transverse magnetic field applied along the (0,1,0) direction. Combining results of inelastic neutron scattering experiments, analytical analysis, and numerical simulations, we precisely studied the $E_8$ excitations appearing in the whole Brillouin zone at $B_c^{1D}\approx 4.7$ T. The energy scan at $Q=(0,0,2)$ reveals a match between the data and the theoretical prediction of energies of multiple $E_8$ excitations. Furthermore, dispersions of the lightest three $E_8$ particles have been clearly observed, confirming the existence of the $E_8$ particles in BaCo$_2$V$_2$O$_8$. Our results lay down a concrete ground to systematically study the physics of the exotic $E_8$ particles.