Organic layered superconductors

Abstract

The recent experimental data on the normal and superconducting properties of organic compounds β-(ET)₂X in comparison with (TMTSF)₂X are analysed. Special attention is paid to the structural pecularities of these crystals, electron band structure, T ² law of resistivity, the superconducting properties near T _c and at low temperatures and the effect of disorder on T _c. It is argued that the term T ² in the resistivity arises from the Coulomb interaction of electrons. The BCS model gives a satisfactory description of superconductivity near T _c but it seems to fail in the region T ≪ T _c in high-T _c compounds such as β_H-(ET)₂I₃ and β-(ET)₂AuI₂. The experimental data on the temperature dependence of the upper critical field and the superconducting gap in these compounds provide evidence in favour of an extremely strong coupling model.