Uniaxial Strain Effect of the Moderately Dimerized Molecular Conductor [beta]-(meso-DMBEDT-TTF)2PF6

The anisotropic band structure and electrical resistivity under uniaxial strain were investigated for the moderately dimerized molecular conductor [beta]-(meso-DMBEDT-TTF)2PF6 [DMBEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene], which has an intermediate electronic state between 3/4-filled and effective 1/2-filled band structures at ambient pressure. The calculated energy overlap of the upper and lower bands increased more rapidly by applying uniaxial strain along the c axis than along the (a-b) axis towards the 3/4-filled band structure, which is related to intersite electronic correlation, and the energy gap between these bands is estimated to be larger with application of uniaxial strain along the (a+b) axis towards an effective 1/2-filled band structure, which is related to intrasite electronic correlation. The electrical resistivity under uniaxial strain along the c axis indicates the semiconducting behavior from 300 K and the superconducting (SC) transitions at 4.6-2.8 K under 0.10-0.41 GPa. On the other hand, the metal-insulator transition is not completely suppressed up to 0.8 GPa and SC transitions appear at 4.5-2.6 K under 0.16-0.45 GPa with uniaxial strain along the (a-b) axis. If this uniaxial strain results in semiconducting behavior and positive magnetoresistance related to intersite correlation, the SC states are observed under hydrostatic pressure, which indicates that the SC state is deeply related to the charge-ordered state.