NaYbS2: A planar spin-1/2 triangular-lattice magnet and putative spin liquid

Platelike high-quality NaYbS2 rhombohedral single crystals with lateral dimensions of a few mm have been grown and investigated in great detail by bulk methods such as magnetization and specific heat, but also by local probes such as nuclear magnetic resonance (NMR), electron-spin resonance (ESR), muon-spin relaxation (mu SR), and inelastic neutron scattering over a wide field and temperature range. Our single-crystal studies clearly evidence a strongly anisotropic quasi-two-dimensional magnetism and an emerging spin-orbit entangled J(eff) = 1/2 state of Yb towards low temperatures together with an absence of long-range magnetic order down to 260 mK. In particular, the clear and narrow Yb ESR lines together with narrow Na-23 NMR lines evidence an absence of inherent structural distortions in the system, which is in strong contrast to the related spin-liquid candidate YbMgGaO4 falling within the same space group R (3) over barm. This identifies NaYbS2 as a rather pure spin-1/2 triangular-lattice magnet and a putative quantum spin liquid.