Type-II character and anisotropic superconductivity in natural superconducting covellite

We report a comprehensive investigation of the superconducting properties of the mineral superconductor covellite (CuS) using high-quality single crystals. First, we establish that CuS is an intrinsic type-II superconductor, correcting its long-standing classification as type-I. Second, a complete set of anisotropic superconducting parameters is determined, including the critical fields, penetration depth and coherence length, which yield a Ginzburg–Landau parameter κ ∼ 1.5 and a moderate anisotropy of γ ∼ 2. Our results indicate that this type-II superconductivity can be well-described by a conventional, weak-coupling, single-band s-wave pairing mechanism. This work fills a long-standing gap in the understanding of this archetypal superconductor.