Superconductivity in Metal-Rich Chalcogenide Ta₂Se

The metal-metal bond in metal-rich chalcogenide is known to exhibit various structures and interesting physical properties. Ta₂Se can be obtained by both arc-melting and solid-state pellet methods. Ta₂Se crystallizes a layered tetragonal structure with space group P4/nmm (No. 129; Pearson symbol tP6). 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 Ta₂Se, which together indicate bulk superconductivity with T_c = 3.8(1) K. According to first-principles calculations, the d orbitals in Ta atoms dominate the Fermi level in Ta₂Se. The flat bands at the Δ 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 Ta₂Se.