Strongly scattered phonon heat transport of the candidate Kitaev material Na2Co2TeO6

We studied the field-dependent thermal conductivity (kappa) of Na2Co2Te6, a compound considered as the manifestation of the Kitaev model based on the high-spin d(7) Co2+ ions. We found that in-plane magnetic fields beyond a critical value B-c approximate to 10 T are able to drastically enhance. at low temperatures, resulting in a double-peak structure of kappa(T) that closely resembles the behavior of alpha-RuCl3. This result suggests that heat transport in Na2Co2TeO6 is primarily phononic, and it is strongly affected by scattering from magnetic excitations that are highly tunable by external fields. Interestingly, for magnetic fields B parallel to a (i.e., along the zigzag direction of the Co-Co bonds), there is an extended field range which separates the long-range magnetic order for B <= B-c approximate to 10 T and the partially spin-polarized gapped high-field phase for B greater than or similar to 12 T. The low-energy phonon scattering is particularly strong in this field range, consistent with the notion that the system becomes a quantum spin liquid with prominent spin fluctuations down to energies of no more than 2 meV.

Automated summary

The study reveals that Na2Co2TeO6 is significantly enhanced by in-plane magnetic fields at low temperatures, showing a double-peak structure in thermal conductivity similar to α-RuCl3. The magnetic field strongly affects the phonon transport in Na2Co2TeO6, displaying characteristics of a quantum spin liquid.