Uniaxial Strain Effect on the θ-Phase Organic Conductor with a Large Dihedral Angle, θ-(TMET-TTP)4PF6

For the organic conductor θ-(TMET-TTP) 4 PF 6 (TMET-TTP: 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-5-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene), electrical resistance has been measured under the uniaxial strain applied along the a -, b -, and c -axes as well as under hydrostatic pressure. Contrary to the prediction of the universal phase diagram in which the c -axis strain will raise the metal–insulator transition temperature by expanding the dihedral angle, the insulating state is suppressed under the strain in all directions. The results are interpreted in terms of the increasing intra-stack transfer integral in the large dihedral angle region.