PRESSURE EFFECT ON SUPERCONDUCTIVITY IN THE ORGANIC-CRYSTAL FAMILY KAPPA-(BEDT-TTF)2CU[N(CN)2]CL1-XBRX

The influence of hydrostatic pressure on superconductivity (SC) in a s eries of four compounds kappa-(BEDT-TTF)2 Cu[N(CN)2]-Cl1-xBrx, with x= 0.15 0 2, 0.3 and 1.0 has been studied by measurements of the static d iamagnetic shielding- and Meissner-magnetization. Different behavior o f the SC volume fraction and of T(c) versus pressure is found for two regions of T-P-x Phase diagram. Region I (P greater-than-or-equal-to 0 for x greater-than-or-equal-to 0.3, and P > 250 bar for x less-than-o r-equal-to 0.2) is characterized by a rapid decrease of Tc and by a pr essuure-independent SC volume fraction. In a region II(x less-than-or- equal-to 0.2, P<250 bar), where the SC phase has, according to resisti vity data, a common border with the insulating phase, a rapid increase of both T(c) and the SC fraction with pressure is observed.