Low-temperature specific heat of the superconductor Mo3Sb7

The low-temperature specific heat of a superconductor Mo3Sb7 with T-c = 2.2 +/- 0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient gamma(n), and the Debye temperature Theta(D) are found to be 34.5(2) mJ mol(-1) K-2 and 283(5) K, respectively. The enhanced gamma(n) 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 2 Delta(1)/k(B)T(c) and 2 Delta(2)/k(B)T(c) = 2.5, and relative weights of the molar electronic heat coefficients gamma 1/gamma(n) = 0.7 and gamma(2)/gamma(n) = 0.3. Some characteristic thermodynamic parameters for the studied superconductor. like the specific heat jump at T-c, Delta C(T-c)/gamma T-n(c), the electron-phonon Coupling constant, lambda(c-ph), the upper H-c2 and thermodynamic critical H-c0 fields, the penetration depth lambda, coherence length xi and the Ginzburg-Landau parameter kappa are evaluated. The estimated values of parameters such as 2 Delta(0)/k(B)T(c), Delta C(T-c)/lambda nT(c), N(E-F) and lambda(e-ph) suggest that Mo3Sb7 belongs to all 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. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.