Polytypism, Anisotropic Transport, And Weyl Nodes In The Van Der Waals Metal Tafete4

Layered van der Waals (vdW) materials belonging to the MM'Te-4 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, alpha-TaFeTe4 and beta-TaFeTe4. We find that the structure of alpha-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 beta-TaFeTe4 produces Weyl points in the electronic band structure. Eight Weyl nodes slightly below the Fermi energy are computationally identified for beta-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.