The Intermediate Disordered Phase of Na2Co2TeO6

As a typical topological state of matter with exotic properties, the quantum spin liquid (QSL) loses the long-range magnetic ordering and has caught a lot of attention over the past decades. Recently, the exactly solvable Kitaev model among various theoretical proposals sheds much light on the experimental implementation of QSL and has been an enduring focus. Although exciting progress has been made on the 4d/5d transition metal Ru/Ir Kitaev candidates, such as α-RuCl₃, H₃LiIr₂O₆, ect., the work on the 3d system is limited. Recently, the Kitaev model was extended to the typical 3d Co-compounds with a honeycomb lattice, which presented the strong quantum effect even from the weak spin-orbital coupling. With the measurements of magnetization, heat capacity, thermal conductivity, torque magnetometry, muon spin rotation/relaxation/resonance, and neutron scattering, the magnetic-field effects on the intermediate disordered phase of Na₂Co₂TeO₆ were explored. Through detailed analysis of the effective K-J₁-Γ-Γ′-J₃ model, the continuum spectra were discussed and the importance of the Kitaev-type interactions was clarified. Moreover, a series of work was extended to other Co-honeycomb lattice by replacing Te⁶⁺ ion with Sb⁵⁺ ion and Na⁺ ion with Ag⁺ ion, which regulate the interaction paths between Co²⁺ ions, anisotropy, and so on.