Rich Phase Behaviors in Kitaev Honeycomb Magnet Na₂Co₂TeO₆

Quantum spin liquids based on the exactly solvable Kitaev honeycomb model have attracted considerable interest. In real materials, the realization of Kitaev interactions requires particular combinations of crystal-field environment, spin-orbit coupling, and exchange interactions. A recently proposed honeycomb magnet, Na₂Co₂TeO₆, provided a promising opportunity for realizing the Kitaev model. After performing a combination of spectroscopic and thermodynamic measurements on single crystals of this material, we found that Na2Co2TeO6, surprisingly, goes through several distinct phase transitions at low temperatures and in zero magnetic field. We attribute the complex phase behaviors to the complexity of the underlying interactions. Understanding these newly discovered magnetic phases is likely a prerequisite before the system can be tuned towards quantum spin liquids.