Emergence of high superconductivity in a layered TaS3 crystal

Abstract

Transition metal chalcogenides (TMCs) have attracted increasing attention due to their rich polymorphs and unique properties, i.e. pressure-induced superconductivity. In this work, we systematically investigated the phase diagram, stability, and superconducting properties of Ta–S systems under compression using the first-principles particle-swarm optimization algorithm and linear-response calculations for the electron–phonon coupling (EPC). Our results reveal a novel superconducting TaS₃ structure with space group P2₁/m, which is characterized by layer stacking of eight-coordinated TaS8 hendecahedrons dynamically stable down to ambient conditions. Strikingly, due to the strong EPC with the constant λ ∼ 1.9, the new P2₁/m-TaS₃ displays a critical temperature T_c of 23.6 K at a relatively low pressure of 50 GPa, which is the highest value ever found among the already reported TMCs. The high T_c primarily arises from the nested Fermi surface and the induced phonon softening in the P2₁/m-TaS₃ structure. In addition, we find other stably superconducting Ta–S stoichiometries, Pm2, and Pmm symmetry TaS, and I4/mcm Ta₂S, but with a much lower T_c. Superconductivity in all these compounds can be attributed to the exotic pressure-induced softened phonon modes. Our findings, therefore, provide important information to further understand the intrinsic physics of pressure-driven behaviors in TMCs and related materials.