Unconventional pressure and magnetic field effect on the ground state of the organic quasi-2D metal (BET)_9(ReO_4) centre dot 2THF

摘要

We present (magneto) transport measurements of the quasi-two-dimensional organic metal (BET)_9(REO_4)_4 centre dot 2THF at pressures P of up to 22 kbar and temperatures T >= 1.9 K. A phase transition occurs at P≈3.5 kbar and T=295 K, the higher pressure phase exhibiting a higher 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, leading, at P>14 kbar to a pressure-independent R_N(T). The low-temperature magnetoresistance has an unconventional, non-monotonous dependence on P.