Reflection of a two-gap nature in penetration-depth measurements ofMgB2film

Abstract

The magnetic penetration depth, λ(T ), in the basal plane of a magnesium diboride (MgB2) film was measured using a two-coil mutual inductance technique at 50 kHz. This film has Tc ≃ 38 K, ∆Tc ≤ 1 K, and λ(0) ∼ 1500Å. At low temperatures, λ −2 (T ) shows a clear exponential temperature dependence, indicating s-wave superconducting order parameter symmetry. However, the data are not quantitatively well described by theory assuming a single gap. From the data fit by the full BCS calculation assuming a double gap, the values of the two distinct gaps were obtained: ∆S(0) = 2.61 ± 0.41 meV and ∆L(0) = 6.50 ± 0.33 meV. The contributions of the small and the large gaps to the total superfluid density at T = 0 were estimated to be 21% and 79%, respectively. Finally, we consider the effect of gap anisotropy on the penetration depth measurements, and find that the gap anisotropy does not play a significant role in determining the temperature dependence of the penetration depth.

Precision microwave electrodynamic measurements of K- and Co-dopedBaFe2As2

“…Also worth noting is that within the s ± -wave model with impurity scattering, 51 some low energy quasiparticle excitations can occur leading to a power law-like dependence, such as a density of states proportional to E 2 . The data can be reasonably well described by a twogap s-wave model, 52 which might be an appropriate starting point for a superconductor with multiple Fermi surface sheets. At very low temperatures, the change of superfluid phase stiffness with temperature is dominated by the smallest gap, with the larger gap becoming more apparent at high temperatures.…”

Effects of the two-gap nature on the microwave conductivity of polycrystallineMgB2films with a critical temperature of39KLee1, Lee2, Han3 et al. 2005Phys. Rev. B135150View full textAdd to dashboardCite

“…For instance, both bands are known to play an important role in determining the specific heat of MgB 2 6,7 , and explaining anomalous temperature-dependent anisotropy of the upper critical field 8,9 . Meanwhile Kim et al reported that the measured penetration depth (λ) of MgB 2 is mainly due to the role of the σ-band 10 . Recently, other interesting results have been reported with regard to the microwave conductivity of MgB 2 by Jin et al…”

Effective action approach to the Leggett's mode in two-band superconductors

“…There are currently many indications that the recently discovered MgB 2 superconductor [17] can be described by the classical two-gap model [20,21] which convincingly fits the specific heat [22] and penetration depth measurements [23]. In particular, in [24,25,26] even the values of the coupling constants for the system of equations (22) for the two-gap and two-band model of MgB 2 were given.…”

“…To consider neutral superconductor one can formally set e = 0 in (23), so that the terms with the electric potential ϕ disappear from the equations and we arrive at…”