Low-temperature specific heat of the superconductor Mo3Sb7

Abstract

The low-temperature specific heat of a superconductor Mo 3 Sb 7 with T c = 2.25 ±0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient γ n , and the Debye temperature Θ D are found to be 34.5(2) mJ/molK 2 and 283(5) K, respectively.The enhanced γ n 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 2∆ 1 /k B T c = 4.0 and 2∆ 2 /k B T c = 2.5, and relative weights of the mole electronic heat coefficients γ 1 /γ n = 0.7 and γ 2 /γ n = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at T c , ∆C(T c )/γ n T c , the electron-phonon coupling constant, λ e−ph , the upper H c2 and thermodynamic critical H c0 fields, the penetration depth λ, coherence length ξ and the Ginzburg-Landau parameter κ are evaluated. The estimated values of parameters like 2∆ 0 /k B T c , ∆C(T c )/γ n T c , N (E F ), and λ e−ph suggest that Mo 3 Sb 7 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.

Electronic Band Structure of Ru3Sn7

“…As previously reported, Ru 3 Sn 7 and Mo 3 Sb 7 dier from one another in physical properties. Mo 3 Sb 7 was rstly determined as an ordinary BCS-type superconductor with T c = 2.1 K [2], and its superconducting state may be described by two BCS-like gaps with 2∆ 1 ≈ 4.0 k B T c and 2∆ 2 ≈ 2.5 k B T c [3]. These suggestions are being strengthened by muon spin-rotation µSR studies in the superconducting state [4].…”

“…Several important facts emerge from dierent electronic band structure calculations for Mo 3 Sb 7 [58]. To encourage the interpretation based on two-gapped model, the electronic density of states and Fermi surface data have shown that the 4d-and spelectrons forming two bands dier from one another by the Fermi velocities, and in consequence they contribute dierently to density of state (DOS) at the Fermi level, E F [3,9]. Another interesting result is the appearance of a largest peak of DOS located at around 0.035 eV below E F , pointing to the existence of the Van Hove singularity.…”

Effect of the tetragonal distortion on the electronic structure, phonons and superconductivity in the Mo3Sb7 superconductor

“…[7,8] As far as the superconducting pairing mechanism is concerned, there is no agreement whether Mo 3 Sb 7 is a typical s-wave electron-phonon (BCS) superconductor or some more complex state is realized. Most of the published results [2,3,[9][10][11], including first principles calculations for the cubic phase, [11] support the conventional * email: wiendlocha@fis.agh.edu.pl…”

“…However, various values of the electronic specific heat jump at the transition point were reported, [3,9,12] ∆C/γT c = 1.04−1.56 much smaller, or close to the weakcoupling BCS value 1.43. Moreover, the specific heat in the superconducting state [9,10] and the magnetic field penetration depth [13,14] behaviors were differently analyzed, in terms of either one-or two-gap BCS models. It was also proposed, that antiferromagnetic fluctuations may be responsible for the superconductivity, due to observation of the spin density wave under pressure.…”

“…[3]), 283 K (Ref. [9]) and 248 K (Ref. [12]), we take the middle value, Θ = 283 K, as representative, however this particular choice doesn't change the relative difference between two phases.…”