Pressure-induced superconductivity in the antiferromagnetκ−(ET)2CF3SO3with quasi-one-dimensional triangular spin lattice

We report an antiferromagnetic (AF) ordering at ambient pressure and a superconducting transition under pressure for $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{ET})}_{2}\mathrm{C}{\mathrm{F}}_{3}\mathrm{S}{\mathrm{O}}_{3}$ $\mathrm{[}\mathrm{ET}=\mathrm{bis}$(ethylenedithio)tetrathiafulvalene], which has a two-dimensional electronic system with quasi-one-dimensional triangular spin lattice. At ambient pressure, AF ordering was detected at ${T}_{N}=2.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ by $^{1}\mathrm{H}$ NMR, subsequent to two structural phase transitions at 230 and 190 K. Under hydrostatic pressures, metallic behavior appeared above \ensuremath{\sim}1.1 GPa, and a superconducting transition (maximum onset ${T}_{c}=4.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at \ensuremath{\sim}1.3 GPa) was observed up to 2.2 GPa. Superconductivity was also found under $c$-axis strain, which reduced ${t}^{\ensuremath{'}}/t$, but was absent under $b$-axis strain which increased ${t}^{\ensuremath{'}}/t$.