Role of the dimerized gap due to anion ordering in spin-density wave phase of (TMTSF)₂ClO₄ at high magnetic fields

Magnetoresistance measurements have been carried out along the highly conducting a axis in the field-induced spin-density wave (FISDW) phase of hydrogenated and deuterated (TMTSF)₂ClO₄ for various cooling rates through the anion ordering temperature. With increasing the cooling rate, (i) the high-field phase boundary β_HI, observed at 27 T in hydrogenated samples for slowly cooled, is shifted towards a lower field, (ii) the last semimetallic SDW phase below β_HI is suppressed, and (iii) the FISDW insulating phase above β_HI is enhanced in both salts. The cooling rate dependence of the FISDW transition and of β_HI in both salts can be explained by taking into account the peculiar SDW nesting vector stabilized by the dimerized gap due to anion ordering.