Pressure-Induced Superconductivity of the Quasi-One-Dimensional Organic Conductor (TMTTF)2TaF6

We investigated the superconductivity of (TMTTF)(2)TaF6 (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 (TMTCF)(2)X (C = Se, S, X: monovalent anion) based on (TMTTF)(2)PF6 (T-CO = 70 K and spin-Peierls: SP, T-SP = 15 K) was proposed by Jerome, 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)TaF6, which has the largest octahedral-symmetry counter anion TaF6 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)TaF6 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 = SbF6 (5.4 <= P <= 9 GPa). In addition, when the pressures with maximum SC temperatures are compared between the PF6 and the TaF6 salts, we found that (TMTTF)(2)TaF6 has a 0.75 GPa on the negative pressure side in the T-P phase diagram of (TMTTF)(2)PF6.

Automated summary

We investigated the superconductivity of (TMTTF)(2)TaF6 under high pressure and discovered a superconducting state in a narrower pressure range compared to other salts. The unique pressure characteristics of (TMTTF)(2)TaF6 in the T-P phase diagram of (TMTTF)(2)PF6 were observed.