SPECIFIC-HEAT AND CRITICAL FIELDS OF THE ORGANIC SUPERCONDUCTOR BETA''-(BEDT-TTF)(2)SF5CH2CF2SO3

We report on specific-heat, magnetization, and ac-susceptibility measu rements of beta ''-(BEDT-TTF)(2)SF5CH2CF2SO3, an organic superconducto r with T-c = 4.5 K, where BEDF-TTF stands for bis(ethylenedithio)-tetr athiafulvalene. The jump of the specific heat C at T-c and the exact f orm of the specific-heat difference between C in the superconducting ( B = 0 T) and in the normal (B = 3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupli ng parameter lambda approximate to 1.1. From measurements of C in magn etic fields we extract the upper critical field B-c2(T). Low-field dc- magnetization measurements were used to determine the temperature depe ndence of the lower critical field B-cl. From T-c down to similar to 3 K the characteristic suppression of B-cl(perpendicular to)(T) below t he sensitivity limit is observed.