Orbital frustration and resonating valence bond state in the spin-1/2 triangular lattice LiNiO2

From the Li-7 nuclear magnetic resonance (NMR) and specific heat measuremen ts of LiNiO2, consisting of a spin-1/2 triangular lattice, it is demonstrat ed that the previously suggested spin-glass-like freezing below T-sg = 8 K; which is caused by defects of Li ions; is not the true ground state, but r ather a quantum disordered state is realized without a spin gap. This state is characterized by power-law behavior of the temperature dependence of th e specific heat below 0.5 K. A spin-liquid state with short-range ferromagn etic correlations is suggested from new insight into the frustration of orb ital ordering for doubly degenerate e(g) shells in the triangular lattice.