Observation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>E</mml:mi><mml:mn>8</mml:mn></mml:msub></mml:math> particles in an Ising chain antiferromagnet
Zhao Zhang, Kirill Amelin, Xiao Wang, Haiyuan Zou, Jiahao Yang, U. Nagel, T. Rõõm, T. Dey, Agustinus Agung Nugroho, T. Lorenz, Jianda Wu, Zhe Wang
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 $\mathrm{BaC}{\mathrm{o}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ 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.