Two-dimensional cobalt-based honeycomb oxide ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ is an important candidate for the realization of Kitaev physics and may provide a future platform for quantum computation and quantum technology. Here, for the quasi-two-dimensional ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ single crystals, we present detailed temperature and polarization-dependent inelastic light scattering (Raman) measurements. Our investigation uncovers the Raman spectroscopic signature of underlying multiple phase transitions i.e., a long-range antiferromagnetic transition $\left({\mathrm{T}}_{\mathrm{N}}\right)$ at ∼30 K, a ferroelectric transition $\left({\mathrm{T}}_{\mathrm{FE}}\right)$ at ∼70 K, and a crossover from a pure paramagnetic phase to a quantum paramagnetic phase around ∼150 K reflected in the renormalized self-energy parameters of the Raman active phonon modes. A distinct signature of spin reorientation deep into the antiferromagnetic phase around ${\mathrm{T}}_{\mathrm{SR}}\sim 17$ K is observed, marked by the clear change in the frequency and linewidth slopes. We also observed an asymmetric phonon mode in the low-frequency region, and it appears below the transition temperature ∼50 K, attributed to the magnetic excitations other than the magnon. The Raman signature of multiple crystal-field excitations at low temperature along with lifting of the Kramer's degeneracy is also observed.

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• Ferroelectricity
• Frustrated magnetism
• Phase transitions
• Phonons
• Spin-orbit coupling