The pressure dependence of resistivity for the checkerboard-type charge-ordered (CO) molecular conductor $\beta \text{−}{\left(meso\text{-DMBEDT-TTF}\right)}_2{\text{PF}}_6$ has been investigated. Under the low pressure of 0.6 kbar, the temperature of resistivity minimum $\left(T_{\text{min}}\right)$ falls from 90 K at an ambient pressure to 67 K, and after the resistivity has been increased, the superconducting (SC) transition is observed at 4.6 K. By applying magnetic field, the SC state is suppressed and the large positive magnetoresistance (MR) is demonstrated below $T_{\text{min}}$ in the CO state. Since the positive MR was observed even in the metallic state under high pressures, the summarized pressure-temperature $\left(P-T\right)$ phase diagram reveals that the SC state neighbors to the CO-insulating and charge-fluctuated metallic states.

• Received 1 January 2009

DOI:https://doi.org/10.1103/PhysRevB.80.092508