Electron spin resonance on the spin-1/2 triangular magnet NaYbS.

The delafossite structure of NaYbS contains a planar spin-1/2 triangular lattice of Yb ions and features a possible realisation of a quantum spin-liquid state. We investigated the Yb spin dynamics by electron spin resonance (ESR) in single-crystalline samples of NaYbS. 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 NaYbS is accessible at low fields (<1 T) and is narrow enough for accurate characterisation of the relaxation rate as well as the g factor of the Yb spins.