Quantum spin liquid in the spin- 1 2 triangular antiferromagnet et Me3 Sb [Pd (dmit)2] 2

The family of layered organic salts X [Pd (dmit)2] 2 are Mott insulators and form scalene-triangular spin- 1 2 systems. Among them, Et Me3 Sb [Pd (dmit)2] 2 has a nearly regular-triangular lattice. We have investigated the spin state of this salt by C13 -NMR and static susceptibility measurements. The temperature dependence of the susceptibility is described as that of a regular-triangular antiferromagnetic spin- 1 2 system with an exchange interaction J=220-250 K. The C13 -NMR measurements reveal that there is no indication of either spin ordering/freezing or an appreciable spin gap down to 1.37 K, which is lower than 1% of J. This result strongly suggests that this system is in the quantum spin-liquid state with no appreciable spin gap, which has been long sought after.