Superconductivity in Metal-Rich Chalcogenide TaSe.

The metal-metal bond in metal-rich chalcogenide is known to exhibit various structures and interesting physical properties. TaSe can be obtained by both arc-melting and solid-state pellet methods. TaSe crystallizes a layered tetragonal structure with space group 4/ (No. 129; Pearson symbol 6). Each unit cell consists of four layers of body-centered close-packing Ta atoms sandwiched between two square nets of Se atoms, forming the Se-Ta-Ta-Ta-Ta-Se networks. Herein, we present magnetic susceptibility, resistivity, and heat capacity measurements on TaSe, which together indicate bulk superconductivity with = 3.8(1) K. According to first-principles calculations, the d orbitals in Ta atoms dominate the Fermi level in TaSe. The flat bands at the Γ point in the Brillouin zone yield the van Hove singularities in the density of states around the Fermi level, which is intensified by introducing a spin-orbit coupling effect, and thus could be critical for the superconductivity in TaSe. The physical properties, especially superconductivity, are completely different from those of Ta-rich alloys or transition-metal dichalcogenide TaSe.