Analysis of the high-field evolution of magnetic excitations in α-RuCl3

The antiferromagnetic order of α-RuCl3 can be suppressed by an in-plane magnetic field of approximately 7.5 tesla. Above this critical field, a rather unconventional field-dependence of the magnetic excitations has been reported. More recent Raman and terahertz spectroscopy experiments went up to significantly higher fields [1, 2]. We theoretically analyze these and compare the response of realistic anisotropic models. To this end we discuss different scattering mechanisms for the Raman response. We find that the Fleury-Loudon mechanism (usually discussed as the "two-magnon mechanism") can explain the strikingly strong intensity of the single-magnon in the Raman spectra, as a consequence of strong Kitaev and anisotropic couplings. Our study firmly establishes the partially-polarized quantum disordered character of the high-field phase.

[1] Sahasrabudhe et al., arXiv:1908.11617
[2] Wulferding et al., arXiv:1910.00800

This work was done in collaboration with A. Sahasrabudhe, S. Reschke, R. German, T. C. Koethe, J. Buhot, D. Kamenskyi, C. Hickey, P. Becker, V. Tsurkan, A. Loidl, S. H. Do, K. Y. Choi, M. Grüninger, Z. Wang, and P. H. M. van Loosdrecht.