A route to realize Kitaev quantum spin liquid phase: strain engineering in Cu₃Co₂SbO₆ heterostructure

Efforts to realize the Kitaev quantum spin liquid (QSL) in layered Co²⁺ (3d⁷) honeycomb systems are driven by the QSL’s unique quantum-entangled properties. However, known materials display long-range antiferromagnetic ordering due to lattice distortions, particularly trigonal distortions, which prevent Kitaev QSL formation. To explore this, we investigated the strain dependence of the Néel temperature in Co-based honeycomb oxides, focusing on Cu₃Co₂SbO₆ thin films grown on ZnO (001) substrates. By using heterostructure engineering techniques—such as film thickness control and helium implantation—we modulated the trigonal distortion and crystal field of CoO₆ octahedra. X-ray Diffraction and X-ray Absorption Spectroscopy revealed that changes in out-of-plane lattice parameters affect the trigonal crystal field, resulting in Néel temperatures from 7.8 K to 22.7 K, compared to 16 K in bulk. First-principles calculations indicate that reduced trigonal field enhances geometric frustration, suppressing antiferromagnetic order. These findings underscore the potential of strain-engineered cobaltate heterostructures for realizing Kitaev QSLs in honeycomb lattices.