Superconductivity in Metal-Rich Chalcogenide Ta₂Se

Abstract

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 <i>P</i>4/<i>nmm</i> (No. 129; Pearson symbol <i>tP</i>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 Ta₂Se, which together indicate bulk superconductivity with <i>T</i>_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 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 Ta₂Se. The physical properties, especially superconductivity, are completely different from those of Ta-rich alloys or transition-metal dichalcogenide TaSe₂.