Filled skutterudite superconductor CaOs4P12 prepared by high-pressure synthesis

In this paper, we report the transport, thermodynamic, and superconducting properties of a new filled skutterudite CaOs4P12 synthesized under high pressure and high temperature. The electrical resistivity of 3.4–4.8 mΩcm, carrier concentration of 3.8–6.1 × 1020cm−3 , and positive Hall coefficient suggest that CaOs4P12 is a semimetal with hole carriers. An anomaly due to low-energy optical modes corresponding to an Einstein temperature of 150 K was observed in the specific heat. Resistivity, dc magnetic susceptibility, and specific heat measurements indicate bulk superconductivity below 2.5 K. The specific heat anomaly at Tc, ∆C/γTc ≈ 1.4, is in agreement with the BardeenCooper-Schrieffer (BCS) value of 1.43. The electron-phonon coupling constant λep is estimated to be 0.47. CaOs4P12 is classified as a BCS-type, weakly coupled type-II superconductor with an upper critical field of Hc2 ≈ 22 kOe and Ginzburg-Landau coherence length of ξ ≈ 12 nm