Quantum Critical Dynamics of a Heisenberg-Ising Chain in a Longitudinal Field: Many-Body Strings versus Fractional Excitations

Zhe Wang; M. Schmidt; A. Loidl; Jianda Wu; Haiyuan Zou; Wang Yang; Chao Dong; Y. Kohama; K. Kindo; D. I. Gorbunov; S. Niesen; O. Breunig; J. Engelmayer; T. Lorenz

doi:10.1103/PhysRevLett.123.067202

paper

Quantum Critical Dynamics of a Heisenberg-Ising Chain in a Longitudinal Field: Many-Body Strings versus Fractional Excitations

arXiv:1903.05492 · doi:10.1103/PhysRevLett.123.067202

Abstract

We report a high-resolution terahertz spectroscopic study of quantum spin dynamics in the antiferromagnetic Heisenberg-Ising spin-chain compound BaCo $_{2}$ V $_{2}$ O $_{8}$ as a function of temperature and longitudinal magnetic field. Confined spinon excitations are observed in an antiferromagnetic phase below $T_{N} ≃ 5.5$ K. In a field-induced gapless phase above $B_{c} = 3.8$ T, we identify many-body string excitations as well as low-energy fractional psinon/antipsinon excitations by comparing to Bethe-Ansatz calculations. In the vicinity of $B_{c}$ , the high-energy string excitations are found to be dynamically dominant over the fractional excitations.

6 pages, 4 figures