Pressure-Induced Superconductivity of the Quasi-One-Dimensional Organic Conductor (TMTTF)<sub>2</sub>TaF<sub>6</sub>

We investigated the superconductivity of (TMTTF)<sub>2</sub>TaF<sub>6</sub> (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...

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Bibliographic Details
Main Authors: Miho Itoi, Toshikazu Nakamura, Yoshiya Uwatoko
Format: Article
Language:English
Published: MDPI AG 2022-07-01
Series:Materials
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Online Access:https://www.mdpi.com/1996-1944/15/13/4638
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Summary:We investigated the superconductivity of (TMTTF)<sub>2</sub>TaF<sub>6</sub> (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 (<i>T</i>-<i>P</i>) diagram of (TMT<i>C</i>F)<sub>2</sub><i>X</i> (<i>C</i> = Se, S, <i>X</i>: monovalent anion) based on (TMTTF)<sub>2</sub>PF<sub>6</sub> (<i>T</i><sub>CO</sub> = 70 K and spin-Peierls: SP, <i>T</i><sub>SP</sub> = 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)<sub>2</sub><i>X</i> (TMTTF)<sub>2</sub>TaF<sub>6</sub>, which has the largest octahedral-symmetry counter anion TaF<sub>6</sub> in the (TMTTF)<sub>2</sub><i>X</i> series, possesses the highest charge-ordering (CO) transition temperature (<i>T</i><sub>CO</sub> = 175 K) in (TMTTF)<sub>2</sub><i>X</i> and demonstrates an anti-ferromagnetic transition (<i>T</i><sub>AF</sub> = 9 K) at ambient pressure. A superconducting state in (TMTTF)<sub>2</sub>TaF<sub>6</sub> emerged after a metal-insulator transition was suppressed with increasing external pressure. We discovered a superconducting state in 5 ≤ <i>P</i> ≤ 6 GPa from <i>T</i><sub>c</sub> = 2.1 K to 2.8 K, whose pressure range is one-third narrower than that of <i>X</i> = SbF<sub>6</sub> (5.4 ≤ <i>P</i> ≤ 9 GPa). In addition, when the pressures with maximum SC temperatures are compared between the PF<sub>6</sub> and the TaF<sub>6</sub> salts, we found that (TMTTF)<sub>2</sub>TaF<sub>6</sub> has a 0.75 GPa on the negative pressure side in the <i>T</i>-<i>P</i> phase diagram of (TMTTF)<sub>2</sub>PF<sub>6</sub>.
ISSN:1996-1944