Breakdown of Magnons in α-RuCl3*

Intensive study of α-RuCl₃ has been motivated recently by signatures of strongly anisotropic and frustrated interactions reminiscent of the Kitaev honeycomb model. Even in the zigzag magnetically ordered state, α-RuCl₃ exhibits a broad continuum of magnetic excitations, which is inconsistent with conventional magnons [1]. Many works have taken the breakdown of magnons as a signature of proximity to the Kitaev spin liquid. By analogy, the suppression of magnetic order at finite magnetic field has been discussed in terms of a field-induced spin-liquid state [2,3,4]. In order to evaluate these proposals, we have considered the dynamical response and stability of magnons at zero and finite field with respect to the full range of realistic magnetic interactions suggested by recent ab-initio calculations. Combining extensive exact diagonalization studies with semiclassical analysis [5,6], we will address the (i) relevant mechanisms for magnon breakdown, (ii) origin and robustness of the continuum, (iii) evolution of the spectra under applied field, and (iv) nature of the field-induced state.
[1] A. Banerjee et al, Science 356, 6342, 1055-1059 (2017).
[2] R. Yadav et al, Sci. Rep. 6, 37925 (2016).
[3] S.-H. Baek et al, Phys. Rev. Lett. 119, 037201 (2017).
[4] A. Banerjee et al, arXiv:1706.07003 (2017).
[5] S. M. Winter et al, Nat. Comm. 8, 1152 (2017).
[6] S. M. Winter et al, arXiv:1707.08144 (2017).