Uniaxial strain effects in the conducting Pd(dmit)2 system (dmit=1,3-dithiol-2-thione-4,5-dithiolate)

Uniaxial strain effects in the two-dimensional strongly correlated electron system with the dimer structure, beta'-(cation)[Pd(dmit)(2)](2) (cation = Me4Sb, Et2Me2P), are described. These salts are Mott insulators at ambient pressure. Under hydrostatic pressure, the insulating state is suppressed and the metallic state accompanied by the superconductivity appears. We have demonstrated that the uniaxial strain along the crystallographic b-axis induces the superconductivity more effectively than the hydrostatic pressure. When the Et2Me2P salt is compressed along the b-axis (p(b)), the superconductivity appears at 6.1 K for p(b) = 4.5 kbar. In the Me4Sb salt, on the other hand, the superconductivity is observed at 8.4 K for p(b) = 4.5 kbar. In each salt, the critical temperature is enhanced and the critical pressure is reduced, compared with those under hydrostatic pressure. The effect of the b-axis strain on interdimer interactions has been simulated by the extended Huckel method, which indicates that the b-axis strain effectively enhances the band width and reduces the correlation effect.