We present evidence of type-I superconductivity in single crystals of ScGa${}_3$ and LuGa${}_3$, from magnetization, specific heat, and resistivity measurements: low critical temperatures $T_c=2.1$–2.2 K; field-induced second- to first-order phase transition in the specific heat, critical fields less than 240 Oe; and low Ginzburg-Landau coefficients $\kappa$ $\approx$ 0.23 and 0.30 for ScGa${}_3$ and LuGa${}_3$, respectively, are all traits of a type-I superconducting ground state. These observations render ScGa${}_3$ and LuGa${}_3$ two of only several type-I superconducting compounds, with most other superconductors being type II (compounds and alloys) or type I (elemental metals and metaloids).

• Received 31 December 2011

DOI:https://doi.org/10.1103/PhysRevB.85.174514