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

Abstract

To clarify the electronic state in a two-dimensional triangular lattice LiVS₂, we have performed ⁵¹V- and ⁷Li-NMR measurements. Below the phase transition temperature T_c of about 310 K from the paramagnetic state to a nonmagnetic state, the Knight shift of both ⁵¹V and ⁷Li does not depend on temperature. The ⁵¹V and ⁷Li spin–lattice relaxation rates 1⁄T₁ 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 ⁷Li 1⁄T₁ 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.