Low-temperature specific heat of the superconductor Mo3Sb7
Abstract
The low-temperature specific heat of a superconductor Mo3Sb7 with Tc = 2.25 (0.05) K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient gamman, and the Debye temperature ThetaD are found to be 34.5(2) mJ/molK2 and 283(5) K, respectively. The enhanced gamman value is interpreted 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 2Delta1/kBTc = 4.0 and 2Delta2/kBTc = 2.5, and relative weights of the mole electronic heat coefficients gamma1/gamman = 0.7 and gamma2/gamman = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at Tc, DeltaCp(Tc)/gammanTc, the electron-phonon coupling constant,lambdaeph, the upper Hc2 and thermodynamic critical Hc0 fields, the penetration depth, lambda, coherence length xi, and the Ginzburg-Landau parameter kappa are evaluated. The estimated values of parameters like 2Delta/kBTc, DeltaCp(Tc)/gammanTc, N(EF), and lambdaeph suggest that Mo3Sb7 belongs to 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 there is no overlapping between the Mo- 4d and Sb-sp orbitals.