Pressure-Induced Superconductivity of the Quasi-One-Dimensional Organic Conductor (TMTTF) 2 TaF 6 .

We investigated the superconductivity of (TMTTF) 2 TaF 6 (TMTTF: tetramethyl-tetrathiafulvalene) by conducting resistivity measurements under high pressure up to 8 GPa. A cubic anvil cell (CAC) pressure generator, which can produce hydrostatic high-pressure, was used for this study. Since the generalized temperature-pressure ( T - P ) diagram of (TMT C F) 2 X ( C = Se, S, X : monovalent anion) based on (TMTTF) 2 PF 6 ( T CO = 70 K and spin-Peierls: SP, T SP = 15 K) was proposed by Jérome, exploring superconductivity states using high-pressure measurement beyond 4 GPa has been required to confirm the universality of the electron-correlation variation under pressure in (TMTTF) 2 X (TMTTF) 2 TaF 6 , which has the largest octahedral-symmetry counter anion TaF 6 in the (TMTTF) 2 X series, possesses the highest charge-ordering (CO) transition temperature ( T CO = 175 K) in (TMTTF) 2 X and demonstrates an anti-ferromagnetic transition ( T AF = 9 K) at ambient pressure. A superconducting state in (TMTTF) 2 TaF 6 emerged after a metal-insulator transition was suppressed with increasing external pressure. We discovered a superconducting state in 5 ≤ P ≤ 6 GPa from T c = 2.1 K to 2.8 K, whose pressure range is one-third narrower than that of X = SbF 6 (5.4 ≤ P ≤ 9 GPa). In addition, when the pressures with maximum SC temperatures are compared between the PF 6 and the TaF 6 salts, we found that (TMTTF) 2 TaF 6 has a 0.75 GPa on the negative pressure side in the T - P phase diagram of (TMTTF) 2 PF 6 .