Unconventional pressure and magnetic field effect on the ground state of the organic quasi-2D metal (BET)(9)(ReO4)(4)center dot 2THF

We present (magneto)transport measurements of the quasi-two-dimensional org anic metal (BET)(9)(REO4)(4). 2THF at pressures P of up to 22 kbar and temp eratures T greater than or equal to1.9 K. A phase transition occurs at P ap proximate to3.5 kbar and T=295 K, the higher pressure phase exhibiting a hi gher resistance, At lower pressures, this phase is semiconductor-like, but on cooling it is converted into a metallic one that is stable down to 20-50 K depending on pressure. Further increases of P stabilize this state, lead ing, at P > 14 kbar to a pressure-independent R-N(T). The low-temperature m agnetoresistance has an unconventional, non-monotonous dependence on P.