Pressure-induced superconductivity and Mott transition in spin-liquid κ-(ET)2Cu2(CN)3 probed by 13C NMR

Pressure-induced superconductivity and Mott transition in the spin-liquid Mott insulator kappa-(ET)(2)Cu-2(CN)(3) have been investigated by C-13 NMR measurements. The Mott transition from the spin liquid to the Fermi liquid is observed as a sudden decrease in 1/T1T, where T-1 is the nuclear-spin-lattice relaxation time. Pseudogap behavior is absent in the Fermi-liquid state, unlike in the metallic phase adjacent to the antiferromagnetic Mott insulator. In the superconducting state, 1/T-1 have a cubic temperature dependence with no Hebel-Slichter peak, which is consistent with non-s-wave superconducting pairing.