A tale about discovery of quantum E8 particles in quantum material BaCo2V2O8
e-mail: oshikawa@issp.u-tokyo.ac.jpLanguage in Speech : English
Exotic thermodynamics and excitations can emerge in the vicinity of a quantum phase transition. In the talk, I will first detailedly discuss the unique quantum criticality for the Grüneisen ratio in the transverse field Ising chain (TFIC) [1]. The unique quantum criticality of the Grüneisen ratio then serves as a smoking gun to identify the underlying TFIC universality observed in quasi-1D antiferromagnetic materials BaCo2V2O8 with transverse field applied along [110] direction [2]. From systematic quantum critical analysis for the effective model of the material SrCo2V2O8 [3], we confirm the material with field applied along [100] direction can also accommodate the TFIC universality with much weaker magnetic field [4]. Furthermore, when the quantum critical point of the TFIC is perturbed by a longitudinal magnetic field, it was predicted that its massive excitations are precisely described by the exceptional E8 Lie algebra. Here we first discuss non-trivial low temperature local spin dynamics of the exotic E8 model [5]. Then we show an unambiguous experimental realization of the E8 physics in the material BaCo2V2O8, via nuclear magnetic resonance and inelastic neutron scattering measurements, and detailed theoretical analysis [6 – 9]. The large separation between the masked 1D and 3D quantum critical points of the system allows us to identify, for the first time, the full 8 single-particle E8 excitations, various multi-E8-particle states [7, 8] as well as the dispersion of E8 particles [9] in the spin excitation spectrum. Our results open new experimental and theoretical routes for exploring the dynamics of quantum integrable systems and physics beyond integrability, and thus bridge key physics in condensed matter and statistical field theory.
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