Magnetoelastic coupling and effects of uniaxial strain in α-RuCl₃ from first principles

Kitaev materials are prime examples where the orbital and spin degrees of freedom can not be understood separately, and instead are formulated jointly through so-called "pseudospins". In contrast to conventional spin-lattice coupling, the spin-orbital nature of the pseudospins foreshadows a much more intricate coupling to the lattice.
Using large-scale first-principles simulations we obtain a magnetoelastic Hamiltonian of α-RuCl₃, that reveals a highly nontrivial interplay of different magnetic interactions with the lattice¹. We reproduce and explain recently measured magnetostriction², using exact diagonalization on our magnetoelastic model, disentangling contributions related to different anisotropic interactions and g factors.
Uniaxial strain perpendicular to the honeycomb planes is predicted to reorganize the relative coupling strengths, strongly enhancing the Kitaev interaction while simultaneously weakening the other anisotropic exchanges under compression. Uniaxial strain may therefore pose a fruitful route to experimentally tune α-RuCl₃ nearer to the Kitaev limit.

[1] D.A.S Kaib, S. Biswas, K. Riedl, S.M. Winter, R. Valenti, arXiv: 2008.08616 (2020).
[2] S. Gass et al., PRB 101, 245158 (2020).