${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ has been proposed as a candidate for realizing the Kitaev quantum spin liquid (QSL). Its intriguing magnetic properties have motivated extensive investigations into its ground state and spin excitation spectrum. A central question concerns whether an in-plane magnetic field can stabilize a QSL state with fractionalized excitations prior to full spin polarization. Using time-domain terahertz spectroscopy, we systematically study the magnetic excitations in ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ within the field-induced intermediate state regime (6 T $<B<$ 10 T). At 5 K, we observe a broad excitation feature superimposed on multiple sharp modes corresponding to magnons. Field-dependent measurements reveal that both the sharp modes and the continuum exhibit magnetic dipole activity. However, their temperature evolution is different. Temperature-dependent measurements at 10 T demonstrate that the sharp modes disappear abruptly near 15 K, consistent with the expected phase boundary. Conversely, the continuum intensity maximizes at this temperature and persists up to at least 40 K. The survival of the broad excitation continuum above the ordering temperature suggests strong spin correlations and quantum fluctuations in this regime.

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• Frustrated magnetism
• Quantum spin liquid
• Spin dynamics
• Terahertz spectroscopy