Critical Field Anisotropy in an Organic Superconductor β-(BEDT-TTF)2I3

A measurement of the anisotropy of the upper critical field H c2 in an organic surerconductor β-(BEDT-TTF) 2 I 3 is reported. A large anisotropy is observed with high critical fields when the magnetic field is applied in the crystallographic a - b plane and a low critical field in the perpendicular direction. ( H c 2 a =9.7 kOe, H c 2 b ′ =9.3 kOe, H c 2 c * =460 Oe at 0.5 K) The result is expressed in terms of the anisotropic coherence lengths and transfer integrals, winch corroborate the two dimensional character of the electronic structure in this organic superconducting material.