Suppression of Antiferromagnetic Order by Strain in Honeycomb Cobaltate: Implication for Quantum Spin Liquid

Recently, layered honeycomb cobaltates have been predicted as a new promising system for realizing the Kitaev quantum spin liquid, a many-body quantum entangled ground state characterized by fractional excitations. However, these cobaltates, similar to other candidate materials, exhibit classical antiferromagnetic ordering at low temperatures, which impedes the formation of the expected quantum state. Here, we demonstrate that the control of the trigonal crystal field of Co ions is crucial to suppress classical antiferromagnetic ordering and to locate its ground state in closer vicinity to quantum spin liquid in layered honeycomb cobaltates. By utilizing heterostructure engineering on Cu3Co2SbO6 thin films, we adjust the trigonal distortion of CoO6 octahedra and the associated trigonal crystal field. The original N\'eel temperature of 16 K in bulk Cu3Co2SbO6 decreases (increases) to 7.8 K (22.7 K) in strained Cu3Co2SbO6 films by decreasing (increasing) the magnitude of the trigonal crystal fields. Our experimental finding substantiates the potential of layered honeycomb cobaltate heterostructures and strain engineering to accomplish the extremely elusive quantum phase of matter.