Speaker
Description
The transverse field Ising chain (TFIC) at its quantum critical point (QCP) in the scaling limit turns to be a central charge 1/2 conformal field theory (CFT). In the vicinity of a small longitudinal magnetic field, eight quasiparticles emerge and the whole system can be described by exceptional $E_{8}$ Lie algebra. This excitation essentially arises from weak confinement due to the perturbation, such that can be treated as meson excitations from two quarks, originally from the idea of McCoy and T. T. Wu. In such a case, this perturbed CFT becomes an integrable field theory (IFT). By calculating the form factor of this IFT, spectrum of multi-$E_{8}$ particle channel can be obtained analytically. Experimentally, the TFIC universality class with longitudinal field perturbation is necessary to realize this $E_{8}$ excitation, which can be achieved in the material BaCo$_2$V$_2$O$_8$ near its QCP. In this talk, I will introduce form factor theory and the spectra analytical properties of this IFT, then show this spectrum in spin dynamical experiments in the material BaCo$_2$V$_2$O$_8$. The results show great power of universality class, bridge the key physics of condensed matter physics, statistical field theory and conformal field theory.
