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

Abstract

We present (magneto)transport measurements of the quasi-two-dimensional organic metal (BET) 9 (REO 4 ) 4 .2THF at pressures P of up to 22 kbar and temperatures 7≥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 khar to a pressure-independent R N (T). The low-temperature magnetoresistance has an unconventional, non-monotonous dependence on P.