Pressure-induced superconductivity and isosymmetric structural transition in quasi-one-dimensional Ta2PdS6

Quasi-one-dimensional materials are a promising system for future applications in electronics and optoelectronics. The refinement of the strong interaction mechanism in quasi-one-dimensional crystals under extreme conditions is still challenging. Here we report a thorough study of superconductivity and phase transition in pressurized ${\mathrm{Ta}}₂{\mathrm{PdS}}₆$ by electrical transport, in situ x-ray diffraction (XRD), Raman spectroscopy, and density functional calculation. ${\mathrm{Ta}}₂{\mathrm{PdS}}₆$ experiences valence bands crossing the Fermi level to form a set of small hole pockets at $P\ensuremath{\sim}3.7$ GPa, which drives the system from a semiconductor to a metal. The pressure-induced superconductivity occurs with decreasing temperature, accompanied by a monoclinic distortion at the critical pressure ${P}_c\ensuremath{\sim}30.8$ GPa. Both XRD measurements and theoretical calculations provide evidence that this structural transition is determined to be isosymmetric, mainly resulting from rearrangement of the S atoms along the $a$ and $c$ axes, indicative of the importance of electron-lattice coupling. When the pressure increases to 82 GPa, the high pressure phase has a very high density of electron states at the Fermi level with ${T}_{\text{c}}^{\text{onset}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 5.2 K, likely mediated by strongly electron-coupled phonons. The present study proposes an alternative approach to investigate the effects of pressure on crystal distortion and superconductivity.