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arXiv · 1903.05492

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
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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 $T_N\simeq 5.5$ 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.

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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. 2019-03-13. Quantum Critical Dynamics of a Heisenberg-Ising Chain in a Longitudinal Field: Many-Body Strings versus Fractional Excitations. https://doi.org/10.1103/physrevlett.123.067202

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