Strain- and pressure-tuned magnetic interactions in honeycomb Kitaev materials

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 (Na2IrO3, beta-Li2IrO3, and alpha-RuCl3). 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.