Crystal growth, superconductivity, and charge density wave of pristine and Pd-intercalated 2H−TaS2

Here, pristine and Pd-intercalated $2H\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{S}}_{2}$ single crystals with ($00l$) orientation were grown by the chemical vapor transport technique. The superconductivity (SC) and charge density wave (CDW) were characterized by magnetic and electrical transport measurements. We find that SC and CDW in the pristine $2H\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{S}}_{2}$ condense respectively at transition temperatures ${T}_{\mathrm{c}}\ensuremath{\sim}0.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{CDW}}\ensuremath{\sim}78\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The CDW order is completely suppressed, and ${T}_{\mathrm{c}}$ is greatly enhanced to 4.5 K in $2H\text{\ensuremath{-}}\mathrm{P}{\mathrm{d}}_{0.04}\mathrm{Ta}{\mathrm{S}}_{2}$, which concludes a competing relation between the two collective electronic states. The positive Hall coefficient ${R}_{\mathrm{H}}$ for both samples above 78 K indicates that hole-type carriers dominate the transport properties, and almost the same ${R}_{\mathrm{H}}$ reveals tiny charge transfer between the intercalant Pd and the host $\mathrm{Ta}{\mathrm{S}}_{2}$. The difference of ${R}_{\mathrm{H}}$ below 78 K between $\mathrm{Ta}{\mathrm{S}}_{2}$ and ${\mathrm{Pd}}_{0.04}\mathrm{Ta}{\mathrm{S}}_{2}$ is attributed to the reconstruction of the Fermi surface by Pd-intercalation-induced collapse of the CDW order. Therefore, the prominently improved ${T}_{\mathrm{c}}$ in $2H\text{\ensuremath{-}}\mathrm{P}{\mathrm{d}}_{0.04}\mathrm{Ta}{\mathrm{S}}_{2}$ is mainly caused by the change of electronic structure due to the suppression of the CDW state rather than charge injection by Pd intercalation.