THEORY OF REENTRANT PHASE-TRANSITION IN BECHGAARD SALT (TMTSF)2CLO4 IN VERY HIGH MAGNETIC-FIELD

The microscopic theory for a spin-density-wave-semimetallic state to a normal-metal one transition in very high magnetic field is proposed. The phase boundary which separates the spin-density-wave (SDW) in an extremely stable state (ESS) from a normal metal, is the line of a 2 1/2 order transition. On this line, the electron pockets on a Fermi surface are created, their size increasing with the magnetic field growing thus leading to a smooth metallization or electron system. The negative temperature slope of a critical line is explained.