Pressure-induced bulk superconductivity in a layered transition-metal dichalcogenide 1T -tantalum selenium

Abstract

We report pressure-driven superconductivity (SC) in the vicinity of a commensurate charge-density wave (CCDW) in transition-metal dichalcogenides (TMDs) $1T\text{\ensuremath{-}}\mathrm{TaS}{\mathrm{e}}_{2}$ by simultaneous resistivity and ac susceptibility. The superconducting phase enters at 4.5 GPa and bulk SC emerges along with the collapse of the CCDW phase at a critical pressure ${P}_{c}\ensuremath{\sim}6.5\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. Higher than ${P}_{c}$, the superconducting transition temperature (${T}_{c}$) keeps increasing linearly, without a dome-shaped superconducting diagram in our pressure range. ${T}_{c}$ reaches $\ensuremath{\sim}5.3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 15 GPa, which is the highest among all $1T$-TMDs. A comprehensive analysis shows that electronic correlations of the CCDW phase open energy gaps, which prohibit Cooper pairing, while the superconducting channels and CCDW domain wall coexist in three dimensions above ${P}_{c}$. The evolutions of the Fermi surface and the softening of phonon modes under pressure are proposed to explain the monotonic increase of ${T}_{c}$. The findings reveal the interplay of CCDW and SC in $1T\text{\ensuremath{-}}\mathrm{TaS}{\mathrm{e}}_{2}$ by a clean method, viz., high pressure, and shed light on the underlying superconducting mechanism in the relevant systems.