CRITICAL FIELDS OF THE AMBIENT PRESSURE STABLE SUPERCONDUCTING STATE AT 8K OF THE ORGANIC METAL ALPHA-T-(BEDT-TTF)2I3

Crystals of αt-(BEDT-TTF)2I3 are organic metals with a stable 8K superconducting transition at ambient pressure. The upper critical fields Hc2 of αt-(BEDT-TTF)2I3 were determined in dependence of the temperature and of the angle of the magnetic field with respect to the various crystal axes, by measuring the mid-transition of the resistivity as well as of the rf penetration depth (ac-susceptibility). The values obtained by both methods agree quite well. The data were analyzed with the anisotropic effective mass model. The highly two dimensional nature of the metal is confirmed, but in the temperature dependence of the critical field with the magnetic field parallel to the ab- plane a crossover from a three- to a two-dimensional behavior is observed.