Quantum spin dynamics of the honeycomb magnet K${}_2$Co${}_2$TeO${}_6$ in high magnetic fields

We present terahertz spectroscopic measurements of quantum spin dynamics in the honeycomb magnet K${}_2$Co${}_2$TeO${}_6$ as a function of temperature, polarization and in an external magnetic field applied in the honeycomb plane. Magnetic excitations are resolved below the magnetic ordering temperature of $T_{\text{N}}$ = 12 K. In the applied magnetic field, we reveal characteristic field dependence not only for the magnetic excitations observed at zero field, but also a rich set of modes emerging in finite fields. The observed magnetic excitations exhibit clear dependence on the terahertz polarization, and characteristic features at field-induced phase transitions consistent with our high-field magnetization data. We cannot evidently resolve a continuumlike feature, even when the long-range magnetic order is presumably suppressed in the strong magnetic field, indicating that a Kitaev-type interaction, if existing, is subleading in this compound.