High-field quantum disordered state in α−RuCl3 : Spin flips, bound states, and multiparticle continuum

A. Sahasrabudhe, D. A. S. Kaib, S. Reschke, R. German, T. C. Koethe, J. Buhot, D. Kamenskyi, C. Hickey, P. Becker, V. Tsurkan, A. Loidl, S. H. Do (+6 others)
2020 Physical review B  
Layered α-RuCl 3 has been discussed as a proximate Kitaev spin-liquid compound. Raman and terahertz spectroscopy of magnetic excitations confirms that the low-temperature antiferromagnetic ordered phase features a broad Raman continuum, together with two magnonlike 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
more » ... d by a gapped multiparticle 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 give rise to a pronounced intensity of these features in the Raman spectra. Our Rapid Communication firmly establishes the partially polarized quantum disordered character of the high-field phase.
doi:10.1103/physrevb.101.140410 fatcat:uoinjbq6ene6znmvf7zkwszbfu