Contrasting electronic states of RuI3 and RuCl3

Abstract

The spin-orbital entangled states are of great interest as they hold exotic phases and intriguing properties. Here we use first-principles calculations to investigate the electronic and magnetic properties of RuI${}_3$ and RuCl${}_3$ in both bulk and monolayer cases. Our results show that RuI${}_3$ bulk is a paramagnetic metal, which is in agreement with recent experiments. We find that the Ru${}^{3+}$ ion of RuI${}_3$ is in the spin-orbital entangled $j_{\mathrm{eff}}=\frac{1}{2}$ state. More interestingly, a metal-insulator transition occurs from RuI${}_3$ bulk to monolayer, and this is mainly due to the band narrowing with the decreasing lattice dimensionality and to the Ru-I hybridization altered by the I $5p$ spin-orbit coupling. In contrast, RuCl${}_3$ bulk and monolayer both show Mott-insulating behavior, the Ru${}^{3+}$ ion is in the formal $S=\frac{1}{2}$ and $L=1$ state with a large in-plane orbital moment, and this result well explains the experimental large effective magnetic moment of RuCl${}_3$ and the strong in-plane magnetization. The present work demonstrates the contrasting spin-orbital states and the varying properties of RuI${}_3$ and RuCl${}_3$.

12 pages, 12 figures