  The delafossite structure of NaYbS2 contains a planar spin-1/2 triangular
lattice of Yb3+ ions and features a possible realisation of a quantum
spin-liquid state. We investigated the Yb3+ spin dynamics by Electron Spin
Resonance (ESR) in single-crystalline samples of NaYbS2. Very clear spectra
with a well-resolved and large anisotropy could be observed down to the lowest
accessible temperature of 2.7 K. In contrast to the ESR properties of other
known spin-liquid candidate systems, the resonance seen in NaYbS2 is accessible
at low fields (< 1T) and is narrow enough for accurate characterisation of the
relaxation rate as well as the g factor of the Yb3+ spins.
