Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies

The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with . We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of with a critical pressure of kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T = 1.5 K. As the charge order sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.