Kitaev physics in the two-dimensional magnet NiPSe_{3}

The Kitaev interaction, found in candidate materials such as α-RuCl_{3}, occurs through the metal (M)-ligand (X)-metal (M) paths of the edge-sharing octahedra because the large spin-orbit coupling (SOC) on the metal atoms activates directional spin interactions. Here, we show that even in 3d transition-metal compounds, where the SOC of the metal atom is negligible, heavy ligands can induce bond-dependent Kitaev interactions. In this work, we take as an example the 3d transition-metal chalcogenophosphate NiPSe_{3} and show that the key is found in the presence of a sizable SOC on the Se p orbital, one which mediates the super-exchange between the nearest-neighbor Ni sites. Our study provides a pathway for engineering enhanced Kitaev interactions through the interplay of SOC strength, lattice distortions, and chemical substitutions.