Complex phase diagram of the honeycomb iridate Cu₂IrO₃

The recently synthesized family of intercalated J_eff = 1/2 honeycomb iridates feature promising evidence for hosting the Kitaev quantum spin liquid state. Here, we explore the high-pressure phase diagram of the intercalated honeycomb Cu₂IrO₃ at room temperature and 15 K using x-ray scattering and spectroscopy, as well as ab initio evolutionary structure search¹. Compression below 10 GPa drives a structural phase transition marked by the formation of Ir-Ir dimers that destroy the J_eff orbitals. A discontinuous reduction in interplanar distance occurs around 15 GPa and 30 GPa at room and low temperatures, respectively, but the resulting high-pressure diffraction patterns are markedly different. More importantly, the low temperature phase features a dramatic Cu to Ir electron transfer not seen at room temperature. The potential origins of such large electronic structure temperature dependence and the implications to other honeycomb iridates will be discussed.

1) Fabbris et al., Phys. Rev. B 104, 014102 (2021)