Low-temperature specific heat of the superconductor Mo3Sb7 Original Research Article

The low-temperature specific heat of a superconductor Mo3Sb7 with Tc = 2.2 ± 0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient γn, and the Debye temperature ΘD are found to be 34.5(2) mJ mol−1 K−2 and 283(5) K, respectively. The enhanced γn value is interpreted as due to a narrow Mo-4d band pinned at the Fermi level. The electronic specific heat in the superconducting state can be analyzed in terms a phenomenological two BCS-like gap model with the gap widths 2Δ1/kBTc = 4.0 and 2Δ2/kBTc = 2.5, and relative weights of the molar electronic heat coefficients γ1/γn = 0.7 and γ2/γn = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at Tc, ΔC(Tc)/γnTc, the electron–phonon coupling constant, λe−ph, the upper Hc2 and thermodynamic critical Hc0 fields, the penetration depth λ, coherence length ξ and the Ginzburg–Landau parameter κ are evaluated. The estimated values of parameters such as 2Δ0/kBTc, ΔC(Tc)/γnTc, N(EF) and λe−ph suggest that Mo3Sb7 belongs to an intermediate-coupling regime. The electronic band structure calculations indicate that the density of states near the Fermi level is formed mainly by the Mo-4d orbitals and that there is no overlap between the Mo-4d and Sb-sp orbitals.