Spin-orbit phase behavior of Na2Co2TeO6 at low temperatures

We present a comprehensive study of single crystals of Na2Co2TeO6, a putative Kitaev honeycomb magnet, focusing on its low-temperature phase behaviors. A new thermal phase transition is identified at 31.0 K, below which the system develops a two-dimensional (2D) long-range magnetic order. This order precedes the well-known three-dimensional (3D) order below 26.7 K, and is likely driven by strongly anisotropic interactions. Surprisingly, excitations from the 3D order do not support the order's commonly accepted zigzag nature, and are instead consistent with a triple-q description, which has remained hitherto unexplored in the study of Kitaev honeycomb magnets. The 3D order exerts a fundamental feedback on high-energy excitations that likely involve orbital degrees of freedom, and it features strongly scattered spin waves until at much lower temperatures, a sign for ground state near degeneracy and frustration. These findings constrain microscopic models and render Na2Co2TeO6 a spin-orbit entangled frustrated magnet that hosts very rich physics.

Automated summary

The single crystals of Na2Co2TeO6 exhibit complex low-temperature phase behaviors, including a new thermal phase transition with 2D and 3D long-range magnetic orders. Excitations from the 3D order support a triple-q description, contrary to the commonly accepted zigzag nature, indicating a fundamental feedback on high-energy excitations. These findings suggest Na2Co2TeO6 as a spin-orbit entangled frustrated magnet with rich physics.