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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Ternary compounds containing thorium, copper, and arsenic are of interest for their unique electronic and structural properties.
• Understanding the interplay between different structural motifs and emergent phenomena like superconductivity and charge-density waves is crucial.

Purpose of the Study:

• To synthesize and characterize a novel ternary compound, Th₂Cu₄As₅.
• To investigate its crystal structure and physical properties, including superconductivity and potential charge-density-wave (CDW) transitions.

Main Methods:

• Single crystal X-ray diffraction for structural determination.
• Measurements of electrical resistivity, magnetic susceptibility, and specific heat.
• Hall coefficient measurements to probe charge carrier behavior.
• Band structure calculations to support experimental findings.

Main Results:

• Th₂Cu₄As₅ crystallizes in a tetragonal structure (space group P4/mmm) with lattice parameters a = 4.0639(3) Å and c = 24.8221(17) Å.
• The structure consists of alternating Th₂As₂ fluorite-type layers and Cu₄As₃ antifluorite-type slabs.
• Bulk superconductivity was observed with a transition temperature (T_c) of 4.2 K.
• Anomalies in physical properties at 48 K, including a sign change in the Hall coefficient, indicate a charge-density-wave-like (CDW) phase transition.
• Band calculations suggest superconductivity originates from Cu₄As₃ slabs and the CDW transition from the As plane in Th₂As₂ layers.

Conclusions:

• Th₂Cu₄As₅ is a novel superconductor exhibiting a distinct CDW-like phase transition.
• The distinct structural units (Cu₄As₃ slabs and Th₂As₂ layers) are likely responsible for the observed superconducting and CDW phenomena, respectively.
• This discovery provides new insights into the complex phase behavior of ternary thorium-based intermetallic compounds.