Magnetic excitations in the Kitaev quantum spin liquid candidate Na2Co2TeO6 – Part I: Experiment*

Layered honeycomb magnets have received lots of attention as potential candidates to realize Kitaev physics [1,2]. Among them, Co-based honeycomb Na₂Co₂TeO₆ (NCTO) is recently proposed to be a potential Kitaev material. NCTO is antiferromagnetic ordered below T_N = 25K. A complex temperature-field (T-B) phase diagram with multiple ordered, disordered states is proposed [3]. Here in Part I, we report the low-energy infrared and electron spin resonance spectroscopy measurements on NCTO in a broad range of temperatures and magnetic fields. The measurement results reveal a rich structure of magnetic excitations across the AFM, disordered and polarized states. Such richness of excitations is at variance with presently available theoretical models and suggests that other factors need to be taken into account. The experimental results will be further discussed with theoretical calculations in Part II.

[1] Liu et. al., Phys. Rev. B 97, 014407 (2018)

[2] Liu et. al., Phys. Rev. Lett. 125, 047201 (2020)

[3] Lin  et al. Nat Commun 12, 5559 (2021).