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arXiv · 1706.04181

Experimental Observation of Bethe Strings

Zhe Wang·Jianda Wu·Wang Yang·Anup Kumar Bera·Dmytro Kamenskyi·A. T. M. Nazmul Islam·Shenglong Xu·Joseph Matthew Law·Bella Lake·Congjun Wu·Alois Loidl
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Abstract

Almost one century ago, string states - complex bound states (Wellenkomplexe) of magnetic excitations - have been predicted to exist in one-dimensional quantum magnets and since then become a subject of intensive theoretical study. However, experimental realization and identification of string states in condensed-matter systems remains an unsolved challenge up to date. Here we use high-resolution terahertz spectroscopy to identify string states in the antiferromagnetic Heisenberg-Ising chain SrCo2V2O8 in strong longitudinal magnetic fields. We observe complex bound states (strings) and fractional magnetic excitations (psinons and antipsinons) in the field-induced critical regime, which are precisely described by the Bethe ansatz. Our study reveals that two-string and three-string states govern the quantum spin dynamics close to the quantum criticality, while the fractional excitations are dominant at low energies, reflecting the antiferromagnetic quantum fluctuations.

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Zhe Wang, Jianda Wu, Wang Yang, Anup Kumar Bera, Dmytro Kamenskyi, A. T. M. Nazmul Islam, Shenglong Xu, Joseph Matthew Law, Bella Lake, Congjun Wu, Alois Loidl. 2017-06-13. Experimental Observation of Bethe Strings. https://doi.org/10.1038/nature25466

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