Electronic states of organic quasi-two dimensional conductor β″-(DODHT)2PF6: Charge ordering and superconductivity

In the title compound, we made X-ray satellite reflection measurements up to 0.7 GPa and angle-dependent magnetoresistance (AMR) measurements at 1.9 GPa. The purpose of the study is to clarify (1) how large the temperature-pressure regime is for the long-range charge ordering (CO), (2) whether or not the high pressure regime for the superconductivity is really a metallic state, and (3) what the electronic properties are in the intermediate pressure regime between the long-range CO and the superconducting states. The long-range CO was found to be stable up to 0.7 GPa, and its temperature-pressure regime coincides with that expected from transport measurements. AMR at 1.9 GPa, 1.4 K and 12 T suggests the presence of Fermi surfaces consistent with band calculations based on X-ray structural analyses at room temperature and the same pressure. Raman studies by one of the authors (K.Y.) suggest the presence of metallic state in the intermediate pressure regime where the resistance shows apparently insulating properties. Discussion is made on the role of the charge-degree of freedom in causing the superconductivity.