Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)2GaCl4 (BETS bis(ethylene-dithio)tetraselenafulvalene)

The Fermi-surface topology of the organic superconductor lambda-(BETS)(2)GaCl4 has been determined using the Shubnikov-de Haas and magnetic breakdown effects and angle-dependent magnetoresistance oscillations. The former experiments were carried out in pulsed fields of up to 60 T, whereas the latter employed quasistatic fields of up to 30 T. All of these data show that the Fermi-surface topology of lambda-(BETS)(2)GaCl4 is very similar to that of he most heavily studied organic superconductor, kappa-(BEDT-TTF)(2)Cu(NCS)(2), (BEDT-TTF drop bis(ethylene-dithio)tetrathiafulvalene), except in one important respect: the interplane transfer integral of lambda-(BETS)(2)GaCl4 is a factor similar to5 larger than that of kappa-(BEDT-TTF)(2)Cu(NCS)(2). The increased three-dime,nsionality of k-(BETS)(2)GaCl4 is manifested in radio-frequency penetration-depth measurements, which show a clear dimensional crossover in the behaviour of H-c2(T). The radio-frequency measurements have also been used to extract the Labusch parameter determining the fluxoid interactions as a function of temperature, and to map the flux-lattice melting curve.