Superconducting energy gap distribution in c-axis oriented MgB2 thin film from point contact study

Abstract

We have analyzed about hundred voltage-dependent differential resistance dV /dI(V ) curves of metallic point contacts between c-axis oriented MgB2 thin film and Ag, which exhibit clear Andreev reflection features connected with the superconducting gap. About one half of the curves show the presence of a second larger gap. The histogram of the double gap distribution reveals distinct maxima at 2.4 and 7 meV, while curves with a single-gap features result in more broad maximum at 3.5 meV. The double-gap distribution is in qualitative agreement with the distribution of gap values over the Fermi surface calculated by H. J. Choi et al. (cond-mat/0111183). The data unequivocally show the presence of two gaps ∆S = 2.45 ± 0.15 meV and ∆L = 7.0 ± 0.45 meV in MgB2 with gap ratio ∆L/∆S = 2.85 ± 0.15. Our observations prove further a widely discussed multigap scenario for MgB2, when two distinct gaps are seen in the clean limit, where a single averaged gap is present in the dirty one.

Advances in point-contact spectroscopy: two-band superconductor MgB2 (Review)

“…adjusted gap weighting factor [40]. The second kind is better fitted with a single gap provided an increased depairing parameter Γ (Fig.…”

“…The first one clearly shows two sets of energy gap minima located, as shown in distribution graph of On the lower panel the theoretical distribution is shown. After Naidyuk et al [40].…”

“…The single-band numerical inversion [40]. ∆ L(S) stand for large (small) superconducting energy gap.…”

Point-Contact Spectroscopy of Two-Band Superconductor MgB2

“…These curves are nicely fitted by BTK [26] theory (with a small Γ parameter) for two conducting channels with an adjusted gap weighting factor [27]. Voltage (mV) Figure 1 dV /dI (experimental dots) for 4 contacts between MgB2 thin film and Ag with corresponding BTK fitting (lines) [27]. ∆ L(S) stands for large (small) SC energy gap.…”

“…∆ L(S) stands for large (small) SC energy gap. After Naidyuk et al [27]. The second kind of dV /dI represents only one gap structure and is better fitted with a single gap provided an increased depairing parameter Γ (Fig.…”