Superconductivity at 14.2 K in Layered Organics under Extreme Pressure

We demonstrate that an organic Mott insulator, β'-(BEDT-TTF) 2 ICl 2 , is metallized by application of extremely high pressure by means of the cubic anvil press. When the metallic state is stabilized, superconductivity with the highest transition-temperature ( T c ) among the organic systems appears. The lower limit of the pressure at which the superconducting transition manifests itself is approximately 7.0 GPa and T c reaches a maximum value, 14.2 K (onset), at 8.2 GPa. The pressure-temperature phase diagram is constructed and discussed in terms of the comparison with those of other organic systems.