Anion-Anion Bonding and Topology in Ternary Iridium Tin Selenides

Iridium compounds have been under intense scrutiny due to strong relativistic effects (spin-orbit coupling) which have comparable energy scales to crystal field stabilization and electron correlations, which could lead to non-trivial behavior. Here we report the synthesis, characterization, and physical properties of two new, and one known, Ir-Sn-Se compounds. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low spin 5d$^{\mathrm{6}}$ Ir$^{\mathrm{3+}}$. Furthermore, electronic structures calculations on Ir$_{\mathrm{2}}$Sn$_{\mathrm{3}}$Se$_{\mathrm{3}}$ show a single, spherical, non-spin-orbit split valence band that supports mobile p-type carriers, and imply that Ir$_{\mathrm{2}}$Sn$_{\mathrm{3}}$Se$_{\mathrm{3}}$ is topologically non-trivial under tensile strain, due to inversion of Ir-$d$ and Se-$p$ states.