Organic conductors and superconductors at high field

The organic charge transfer salts (TMTSF)₂X (where X=ClO₄, PF₆, ReO₄, etc.) are among the most remarkable materials discovered. A single crystal of the PF₆ salt exhibits metallic, insulating, antiferromagnetic, spin density wave, and superconducting phases as well as quantum Hall effects (QHE) as temperature, pressure and magnetic field are varied. In addition there are new phenomena found in no other materials: a cascade of magnetic field induced transitions and a new form of quantum oscillations. The QHE is particularly interesting in that it is observed for the first time in a bulk crystal. Unlike the conventional integer effect which arises from noninteracting particles and some disorder, in these salts the QHE is the result of a collective spin density wave distortion which assures that the Fermi energy is always in the gap between Landau bands and the QHE steps are accompanied by first order phase transitions.