Strongly electron-correlated semimetal RuI${}_3$ with a layered honeycomb structure

A polymorph of RuI${}_3$ synthesized under high pressure was found to have a two-layered honeycomb structure. The resistivity of RuI${}_3$ exhibits a semimetallic behavior, in contrast to insulating properties in $\alpha$-RuCl${}_3$. In addition, Pauli paramagnetic behavior was observed in the temperature dependence of a magnetic susceptibility and a nuclear spin-lattice relaxation rate 1/$T_1$. The band structure calculations indicate that contribution of the I 5$p$ components to the low-energy $t_{2\mathrm{g}}$ bands effectively decreases Coulomb repulsion, leading to semimetallic properties. The physical properties also suggest strong electron correlations in RuI${}_3$.