Electrical and structural properties of θ-type BEDT-TTF organic conductors under uniaxial strain

In order to investigate the relationships between crystal structures and electronic properties of theta-type BEDT-TTF organic conductors, electrical properties of theta-(BEDT-TTF)(2)Ag(CN)(2) and theta-(BEDT-TTF)(2)CsZn(SCN)(4) and crystal structures of theta-(BEDT-TTF)(2)CsZn(SCN)(4) tinder uniaxial strain are investigated. The resistivity measurements for both salts tinder uniaxial strain show that the intercolumnar uniaxial strain preserves the metallic nature while the infra-columnar one induces an insulating behavior, which are reminiscent of the charge-ordered state of theta-(BEDT-TTF)(2)RbZn(SCN)(4). Structure analyses of theta-(BEDT-TTF)(2)CsZn(SCN)(4) under uniaxial strain indicate that the inter-columnar strain slightly increases the diagonal transfer integral but does not vary the vertical one. and the infra-columnar uniaxial strain largely increases the vertical transfer integral but does not change the diagonal one. Based on these experimental results, the key parameters to determine the electrical properties of theta-type BEDT-TTF salts are discussed. It is suggested that the transfer integral along the infra-columnar direction dominates the occurence of the charge-ordered state.