Polytypism, Anisotropic Transport, and Weyl Nodes in the van der Waals Metal TaFeTe₄

Layered van der Waals (vdW) materials belonging to the MM'Te₄ structure class have recently received intense attention due to their ability to host exotic electronic transport phenomena, such as in-plane transport anisotropy, Weyl nodes, and superconductivity. Here we report two new vdW materials with strongly anisotropic in-plane structures featuring stripes of metallic TaTe₂ and semiconducting FeTe₂, α-TaFeTe₄ and β-TaFeTe₄. We find that the structure of α-TaFeTe₄ produces strongly anisotropic in-plane electronic transport (anisotropy ratio of up to 250%), outcompeting all other vdW metals, and demonstrate that it can be mechanically exfoliated to the two-dimensional (2D) limit. We also explore the possibility that broken inversion symmetry in β-TaFeTe₄ produces Weyl points in the electronic band structure. Eight Weyl nodes slightly below the Fermi energy are computationally identified for β-TaFeTe₄, indicating they may contribute to the transport behavior of this polytype. These findings identify the TaFeTe₄ polytypes as an ideal platform for investigation of 2D transport anisotropy and chiral charge transport as a result of broken symmetry.