Pressure dependence of the electronic properties of the quasi-two-dimensional organic superconductor β" - (BEDT-TTF)₂SF₅CH₂CF₂SO₃

We report on the pressure-dependent superconducting and transport properties of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene (or ET for short). With increasing pressure the superconducting transition temperature, Tc, decreases monotonously. Superconducting traces can be observed up to 11.7 kbar; at higher pressures an insulating state appears. By use of Shubnikov-de Haas (SdH) and angular-dependent magnetoresistance oscillations the Fermi-surface topology as well as the effective masses were determined. Close to the insulating state a new SdH frequency can be resolved. The effective mass, mc, of the main orbit decreases approximately linear with pressure. By assuming a direct relationship between mc and the superconducting coupling parameter lambda, the pressure dependence of Tc can be well explained by the modi-fied McMillan equation. For all pressures in the metallic state the resistance can be described by R = R0 + AT2 at low temperatures. The coefficient A, however, is found to be not proportional to m2c as expected for a purely electronic origin of the T2 behavior.