The order parameter of spin density wave in the region of observation of the fractional quantum Hall effect in layered quasi-one-dimensional organic metals of a (TMTSF)2 X family

The behavior of spin density wave (SDW) in conducting salts of a (TMTSF)2 X family is studied in superhigh magnetic fields at which the Fractional Quantum Hall Effect (FQHE) is observed. The order parameter of SDW is shown to be proportional to the value of electron (hole) pocket of the Fermi surface and is almost independent of magnetic field along the whole width of the Hall plateau. This is likely to account for the existence of a so-called Extremely Stable State in the phase diagram of (TMTSF)2 Cl O4