E8 Spectra of Quasi-one-dimensional Antiferromagnet BaCo2V2O8 under Transverse Field
Abstract
We report 51V nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) measurements on a quasi-1D antiferromagnet BaCo2V2O8 under transverse field along the [010] direction. The scaling behavior of the spin-lattice relaxation rate above the N\'eel temperatures unveils a 1D quantum critical point (QCP) at Hc1D≈ 4.7 T, which is masked by the 3D magnetic order. With the aid of accurate analytical analysis and numerical calculations, we show that the zone center INS spectrum at Hc1D is precisely described by the pattern of the 1D quantum Ising model in a magnetic field, a class of universality described in terms of the exceptional E8 Lie algebra. These excitations keep to be non-diffusive over a certain field range when the system is away from the 1D QCP. Our results provide an unambiguous experimental realization of the massive E8 phase in the compound, and open new experimental route for exploring the dynamics of quantum integrable systems as well as physics beyond integrability.