Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid (QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh2 (A = alkali or monovalent ions, Re = rare earth, Ch = O, S, Se). The family compounds share the same structure (R3m) as YbMgGaO4, and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO2, NaYbS2 and NaYbSe2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages. This makes the family an ideal platform for fundamental research of QSLs and its promising applications.PACS numbers: 75.10. Kt, 75.30.Et, 75.30.Gw Introduction.-The concept of quantum spin liquids (QSLs) was originally proposed by P. W. Anderson theoretically over 40 years ago [1]. It describes a highly entangled quantum state for spin degrees of freedom and was initially constructed with a superposition of spin singlets on the triangular antiferromagnet, so-called resonatingvalence-bond state [1]. Later on, the possible connection between QSLs and high-temperature superconductivity was theoretically established through doping a QSL Mott insulator [2]. Although the underlying mechanism for the high-temperature superconductivity has not yet come into a consensus, our understanding of QSLs has greatly improved, both from exactly solvable models [3,4] and several classification schemes [4,5]. On the experimental side, various frustrated magnetic materials, particularly the triangular-lattice-based antiferromagnets, were considered to be the most promising systems to realize QSLs [6]. So far, a number of compounds have been reported to host QSLs. Among them, the well-known ones include herbertsmithite and its derived compounds [7][8][9][10][11][12][13][14], and triangular organics [15][16][17][18][19]. The magnetic ions in most of these compounds are 3d transition metal ions Cu 2+ with S = 1/2, which may be crucial to enhance quantum fluctuations.Quite recently, frustrated materials with magnetic rare-earth ions are proposed to be promising QSL candidates [20]. These include the well-known pyrochlore ice materials [21][22][23][24][25][26][27][28][29][30], the kagome magnet [31,32], and the triangular lattice magnets [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. The local degree
