Superconductivity and Charge-Density-Wave-Like Transition in Th₂Cu₄As₅

We report the synthesis, crystal structure, and physical properties of a novel ternary compound, Th₂Cu₄As₅. The material crystallizes in a tetragonal structure with lattice parameters a = 4.0639(3) Å and c = 24.8221(17) Å. Its structure can be described as an alternating stacking of fluorite-type Th₂As₂ layers with antifluorite-type double-layered Cu₄As₃ slabs. The measurement of electrical resistivity, magnetic susceptibility, and specific heat reveals that Th₂Cu₄As₅ undergoes bulk superconducting transition at 4.2 K. Additionally, all these physical quantities exhibit anomalies at 48 K, accompanied by a sign change in the Hall coefficient, suggesting a charge-density-wave-like (CDW) phase transition. Drawing from both experimental data and band calculations, we propose that the superconducting and CDW-like phase transitions are, respectively, associated with the Cu₄As₃ slabs and the As plane in the Th₂As₂ layers.