Spin density wave state in (TMTSF)2ClO4 and fractional quantum hall effect: theory of extremely stable state and reentrant very high field transition

A theory of the extremely stable state (ESS) in which the FQHE in (TMTSF)2ClO4 is observed in very high magnetic fields is proposed. The spin-density-wave (SDW) order parameter in the ESS is independent of the magnetic field: it is proportional to the density of holes in the pockets of the Fermi surface while the value of the SDW gap in the ESS is larger than the hole pocket size. In the ultraquantum limit, the latter increases with the magnetic field growth, and when equal to the gap the reentrant very high field transition occurs. The phase boundary which separates the ESS from a normal metal is the line of the 212-order transition. On this line, electron pockets of the Fermi surface are created thus leading to a smooth metallization. The anomalous width of the ESS is of the order of a basic FQHE plateau size. The negative slope of the transition line between the ESS and the metal state finds its natural explanation.