Magnetoresistance studies on (BEDT-TTF)4(Mo6Cl8)Cl6.xCH2Cl2 under pressure

The charge on the (BEDT-TTF) molecules in the charge-transfer salt (BEDT-TTF)4(Mo6Cl8)Cl6.xCH2Cl2 is not always distributed equally between the two crystallographically inequivalent molecular sites but depends on thermodynamic parameters. To investigate the resulting phase diagram of (BEDT-TTF)4(Mo6Cl8)Cl6.xCH2Cl2, magnetoresistance studies on single crystals were performed at temperatures as low as 800 mK, in fields of up to 16 T and at pressures of up to 1.6 GPa. At ambient pressure this salt shows a metal-insulator (MI) transition at ∼ 40 K that is thought to be due to a spin density wave state. Pressure reduces the MI transition temperature, suppressing it above 1 GPa. The magnetoresistance of this material at moderate pressures is strongly negative with resistance drops of up to 90 % at 16 T and 800 mK. With increasing pressure the magnetoresistance becomes more positive. Between 0.4 GPa to 0.7 GPa the magnetoresistance develops a hysteretic, temperature-independent peak in its field dependence. However, to achieve a positive magnetoresistance pressures in excess of 1.5 GPa are necessary.