Experimental Observation of Quantum Many-Body Excitations of E₈ Symmetry in the Ising Chain Ferromagnet CoNb₂O₆

2020/06/30 by Kirill Amelin, Johannes Engelmayer, Johan Viirok +4 · 1 citation
Physics and Astronomy · #cond-mat.str-el #cond-mat.stat-mech #hep-th

paper · pdf · doi:10.1103/physrevb.102.104431

published as Phys. Rev. B 102, 104431 (2020) · 5 pages, 4 figures. Phys. Rev. B in press

arxiv created 2020/09/09 · arxiv updated 2020/09/25

Abstract

Close to the quantum critical point of the transverse-field Ising spin-chain model, an exotic dynamic spectrum was predicted to emerge upon a perturbative longitudinal field. The dynamic spectrum consists of eight particles and is governed by the symmetry of the E₈ Lie algebra. Here we report on high-resolution terahertz spectroscopy of quantum spin dynamics in the ferromagnetic Ising-chain material CoNb₂O₆. At 0.25 K in the magnetically ordered phase we identify characteristics of the first six E₈ particles, m₁ to m₆, and the two-particle (m₁+m₂) continuum in an applied transverse magnetic field of B_c^1D=4.75 T, before the three-dimensional magnetic order is suppressed above B_c^3D≈ 5.3 T. The observation of the higher-energy particles (m₃ to m₆) above the low-energy two-particle continua features quantum many-body effects in the exotic dynamic spectrum.

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