Semi-Metallic Spin Density Wave Phase in (TMTSF)₂X (X=AsF₆ and PF₆) under Pressure

Abstract

In the spin density wave (SDW) phase of (TMTSF)₂AsF₆ and (TMTSF)₂PF₆, we measured the metal-insulator transition temperature T_MI and the activation energy E_A in the SDW insulating phase under pressure. The ratio 2E_A⁄k_BT_MI near the critical pressure ∼10.5 kbar, above which the SDW phase does not exist, is examined and compared with the mean-field theory developed by Yamaji. We conclude that T_MI does not correspond to the normal-SDW transition temperature T_SDW but is lower than T_SDW. Non-linear conduction with finite threshold was observed above T_MI.