Coexistence of static and dynamic magnetism in the Kitaev spin liquid material Cu2IrO3

Searching for a Kitaev spin liquid phase motivated intense research on the honeycomb iridate materials. However, access to a spin liquid ground state has been hindered by magnetic ordering. Cu₂IrO₃ is a new honeycomb iridate without thermodynamic signatures of a long-range order. Here, we use muon spin relaxation to uncover the magnetic ground state of Cu₂IrO₃. We find a two-component depolarization with slow- and fast-relaxation rates corresponding to distinct regions with dynamic and static magnetism coexisting in the material. X-ray absorption spectroscopy and first-principles calculations identify a mixed copper valence as the origin of this behavior. Furthermore, our results suggest that a minority of Cu²⁺ ions nucleate regions of static magnetism, whereas the majority of Cu⁺/Ir⁴⁺ on the honeycomb lattice give rise to a Kitaev spin liquid.