Phase transition in narrow-band organic metals (BEDT-ATD)2X(solvent) (X=PF6, AsF6, BF4; solvent=THF, DHF, DO)

We present the metal–insulator (MI) transition of the title compounds examined by reflection spectroscopy, X-ray diffraction, and magnetic susceptibility. Below the MI transition temperature, the space group changes from P21/a to Pa with 4kF lattice modulation in (BEDT-ATD)2PF6(DHF) and (BEDT-ATD)2BF4(THF) which undergo MI transitions at 150 K and 200 K, respectively. On the other hand, the symmetry change is not observed at about 80 K in (BEDT-ATD)2PF6(DO) (TMI=100 K), (BEDT-ATD)2PF6(THF) (TMI<50 K), and (BEDT-ATD)2AsF6(THF) (TMI<50 K). The 4kF lattice modulation is supported by the magnetic susceptibility experiment as well. The precursor phenomenon of this structural change is observed already at room temperature in (BEDT-ATD)2PF6(DO). All of these data suggest the view that (BEDT-ATD)2X(solvent) is a strongly correlated 1D metal.