A range of honeycomb-lattice compounds has been proposed and investigated in the search for a topological Kitaev spin liquid. However, sizable Heisenberg interactions and additional symmetry-allowed exchange anisotropies in the magnetic Hamiltonian of these potential Kitaev materials push them away from the pure Kitaev spin-liquid state. Particularly the Kitaev-to-Heisenberg coupling ratio is essential in this respect. With the help of advanced quantum-chemistry methods, we explore how the magnetic coupling ratios depend on strain and pressure in several honeycomb compounds (${\mathrm{Na}}_2{\mathrm{IrO}}_3$, $\beta -{\mathrm{Li}}_2{\mathrm{IrO}}_3$, and $\alpha -{\mathrm{RuCl}}_3$). We find that the Heisenberg and Kitaev terms are affected differently: For strain, in particular, the Heisenberg component decreases more rapidly than the Kitaev counterpart. This provides a scenario where strain can stabilize a spin liquid in such materials.

• Received 7 March 2018
• Revised 31 August 2018

DOI:https://doi.org/10.1103/PhysRevB.98.121107