Enhanced anisotropic superconductivity in the topological nodal-line semimetal InxTaS2

Abstract

Coexistence of topological bands and a charge density wave (CDW) in topological materials has attracted immense attention because of their fantastic properties, such as an axionic CDW, the three-dimensional quantum Hall effect, etc. In this work, the nodal-line semimetal ${\mathrm{In}}_{x}{\mathrm{TaS}}_{2}$ characterized by a CDW and superconductivity is successfully synthesized, whose structure and topological bands (two separated Weyl rings) are similar to ${\mathrm{In}}_{0.58}{\mathrm{TaSe}}_{2}$. A $2\ifmmode\times\else\texttimes\fi{}2$ commensurate CDW is observed at low temperature in ${\mathrm{In}}_{x}{\mathrm{TaS}}_{2}$, identified by transport properties and scanning tunneling microscopy measurements. Moreover, superconductivity emerges below 0.69 K, and the anisotropy ratio of the upper critical field $[\mathrm{\ensuremath{\Gamma}}={H}_{c2}^{||ab}(0)/{H}_{c2}^{||c}(0)]$ is significantly enhanced compared to 2H-${\mathrm{TaS}}_{2}$, which shares the same essential layer unit. According to the Lawrence-Doniach model, the enhanced $\mathrm{\ensuremath{\Gamma}}$ may be explained by the reduced effective mass in the ${k}_{x}\text{\ensuremath{-}}{k}_{y}$ plane, where Weyl rings locate. Therefore, this type of layered topological systems may offer a platform to investigate highly anisotropic superconductivity and to understand the extremely large upper critical field in the bulk or in the two-dimensional limit.