Organic superconductors in the Pauli paramagnetic limit region

The low-dimensionality of the organic superconductors leads the pronounced anisotropy in the upper critical field. In the vicinity of the field direction parallel to the superconducting plane, the critical field shoots out due to the suppression of the orbital pair-breaking effect and is determined by the spin magnetic effect. The organic superconductors are suitable for the study of the high field state related to the spin effect under aligned field, since they are of high crystalline quality. The reported experimental results covering the behavior at low temperature are reviewed first and the breakthrough of the BCS Pauli paramagnetic limit is argued. The in-plane anisotropy of the upper critical field is also touched upon. (orig.)