Trimer V3+ Spin Singlet State and Pseudo Gap in LiVS2 Studied by 51V and 7Li Nuclear Magnetic Resonance

To clarify the electronic state in a two-dimensional triangular lattice LiVS2, we have performed V-51- and Li-7-NMR measurements. Below the phase transition temperature T-c of about 310K frorn the paramagnetic state to a nonmagnetic state, the Knight shift of both V-51 and Li-7 does not depend on temperature. The V-51 and Li-7 spin-lattice relaxation rates 1/T-1 show the exponential temperature dependence below T-c which indicates a gap structure of the electronic state. These results are in agreement with a trimer singlet of V3+ spins below T-c. The increase in Li-7 1/T-1 above T-c indicates the existence of the pseudo gap and agrees with the increase in paramagnetic susceptibility with increasing temperature and with the small entropy change at T-c compared with that in LiVO2.