Triangular-lattice rare-earth chalcogenides $\mathrm{NaYb}{X}_2$ ($X$ = O, S, and Se) are promising quantum spin liquid (QSL) candidates, while the exact properties of the quantum state remain elusive. In this work, we present a spin-dynamic investigation of ${\mathrm{NaYbSe}}_2$. Magnetic susceptibility and specific heat reveal pronounced easy-plane anisotropy and short-range spin correlations below 20 K. In the $X$-band and pulsed high-field electron spin resonance (ESR) measurements, the temperature dependence of anisotropic $g$ factors and linewidths illustrate the development of spin correlations at low temperatures. Interestingly, unlike the noninteracting paramagnets showing linear frequency-field (ν-$H$) behavior through the origin, ${\mathrm{NaYbSe}}_2$ at 2 K exhibits complex dynamical characteristics: The resonance mode evolves from low-field linear ν-$H$ behavior to an easy-plane antiferromagnetic-like (AFM-like) resonance with a gap of 21.06(2) GHz in the intermediate fields and finally reverts to a high-field linear ν-$H$ dependence as the system approaches the magnetic saturation. This phenomenon indicates the suppression of quantum fluctuations by a strong magnetic field, facilitating magnetic-field-induced ordering. Through fitting with the easy-plane AFM-like resonance model, we extracted an effective exchange interaction of $J$ = −1.18 (2) K for ${\mathrm{NaYbSe}}_2$. The ν-$H$ relationship in ESR measurements provides insight for understanding unconventional spin excitations in QSLs of triangular-lattice quantum magnets.

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• High magnetic fields
• Magnetic anisotropy
• Magnetic coupling
• Magnetic interactions
• Magnetism
• Quantum crystals
• Rare-earth magnetic materials
• Strongly correlated systems
• Chemical synthesis
• Crystal growth
• Electron spin resonance
• Specific heat measurements
• X-ray diffraction