Transport properties of alpha double prime -phase organic conductors, (BEDT-TTF) sub(2) CsHg(SCN) sub(4) and (BEDT-TTF) sub(2)K sub(1.4)Co(SCN) sub(4)

摘要

Under pressure, the metal-insulator transition temperature, T sub(MI) (210 K) of alpha double prime -(BEDT-TTF) sub(2)CsHg(SCN) sub(4) (bis(ethylenedithio)tetrathiafulvalene) decreases up to 7 kbar, whereas above this pressure the system becomes more insulating as the pressure increases. This behavior is interpreted in view of the mixed beta double prime -like and theta -like characters of the alpha double prime -phase. In this compound two-fold lattice modulation appears much above T sub(MI), even at room temperature. This indicates that the lattice modulation is not the direct origin of the M-I transition. In alpha double prime -(BEDT-TTF) sub(2)K sub(1.4)Co(SCN) sub(4), T sub(MI) (130 K) rises very slowly under pressure.