Uniaxial strain effect in a strongly correlated two-dimensional system β′−(CH3)4As[Pd(dmit)2]2

Abstract

The molecular conductor ${\beta }^{\prime }-\left({\mathrm{CH}}_3{)}_4\mathrm{As}\right[\mathrm{Pd}(\mathrm{dmit}{)}_2{]}_2$ (dmit=1,3-dithiol-2-thione-4,5-dithiolate) is a two-dimensional system based on the dimer structure. At low temperature, this system is a Mott insulator under ambient and hydrostatic pressure conditions. The electrical resistivities of this system have been measured under uniaxial strain along all three crystallographic axes. When the strain is applied parallel to the b axis within the a-$b$ conducting layer, the nonmetallic behavior is readily suppressed and superconductivity appears at 4 K under 7 kbar. On the other hand, small strain around 2 kbar along both the a- and c-axis directions effectively enhances the nonmetallic behavior. With further increase of the strain, the nonmetallic behavior is suppressed, but cannot be removed even at 15 kbar. These unusual results suggest the crucial role of intra- and interdimer interactions that affect the band width and the effective on-site Coulomb interaction.