Observation of E8 Particles in an Ising Chain Antiferromagnet

TL;DR

This study experimentally observes the predicted E8 particles in a quasi-one-dimensional Ising antiferromagnet using terahertz spectroscopy, confirming the theoretical emergence of E8 symmetry near quantum criticality.

Contribution

First experimental detection of E8 particles in an Ising chain antiferromagnet, validating theoretical predictions of emergent E8 symmetry at quantum critical points.

Findings

Identification of E8 particles via terahertz spectroscopy

Agreement between experimental data and analytical calculations

Observation of two-particle excitations consistent with E8 theory

Abstract

Near the transverse-field induced quantum critical point of the Ising chain, an exotic dynamic spectrum consisting of exactly eight particles was predicted, which is uniquely described by an emergent quantum integrable field theory with the symmetry of the $E_8$ Lie algebra, but rarely explored experimentally. Here we use high-resolution terahertz spectroscopy to resolve quantum spin dynamics of the quasi-one-dimensional Ising antiferromagnet BaCo$_2$V$_2$O$_8$ in an applied transverse field. By comparing to an analytical calculation of the dynamical spin correlations, we identify $E_8$ particles as well as their two-particle excitations.