Layered α-RuCl3 has been discussed as a proximate Kitaev spin liquid compound. Raman and THz spectroscopy of magnetic excitations confirm that the low-temperature antiferromagnetic ordered phase features a broad Raman continuum, together with two magnon-like excitations at 2.7 and 3.6 meV, respectively. The continuum strength is maximized as long-range order is suppressed by an external magnetic field. The state above the field-induced quantum phase transition around 7.5 T is characterized by a gapped multi-particle continuum out of which a two-particle bound state emerges, together with a well-defined single-particle excitation at lower energy. Exact diagonalization calculations demonstrate that Kitaev and off-diagonal exchange terms in the Fleury-Loudon operator are crucial for the occurrence of these features in the Raman spectra. Our study firmly establishes the partially-polarized quantum disordered character of the high-field phase.
@article{arxiv.1908.11617,
title = {High-Field Quantum Disordered State in $\alpha$-RuCl3: Spin Flips, Bound States, and a Multi-Particle Continuum},
author = {A. Sahasrabudhe and D. A. S. Kaib and S. Reschke and R. German and T. C. Koethe and J. Buhot and D. Kamenskyi and C. Hickey and P. Becker and V. Tsurkan and A. Loidl and S. H. Do and K. Y. Choi and M. Grüninger and S. M. Winter and Zhe Wang and R. Valenti and P. H. M. van Loosdrecht},
journal= {arXiv preprint arXiv:1908.11617},
year = {2020}
}