Spin orbit entangled planar J=1/2 triangular lattice magnet NaYbS${}_2$: from a putative spin liquid to field induced magnetic order

Spin orbit coupling (SOC) brought significant progress to the field of quantum spin liquids (QSLs). Having strong spin orbit entanglement promote Yb-based magnets to ideal prime candidates for QSLs and as such NaYbS${}_2$ is a unique model system for planar spin 1/2 triangular lattice magnetism (TLM). In contrast to YbMgGaO${}_4$, which shares the same space group (R-3m) and highlighted as first SOC-TLM-QSL, NaYbS${}_2$lacks inherent lattice distortions and Yb resides on a unique centrosymmetric position in the YbS${}_6$ octahedron. Our comprehensive single crystal study combines bulk- and local- probes and identifies NaYbS${}_2$ as a new spin orbit entangled TLM and putative QSL hosted on a perfect triangular lattice. The application of fields along the (a,b)-plane introduces magnetic order, whereas for fields in the c-direction the system remains unaffected. We present magnetization, specific heat and NMR data down to 300 mK for both directions.