Estimation of Intraband and Interband Relative Coupling Constants from Temperature Dependences of the Order Parameter for Two-Gap Superconductors

Abstract

We present temperature dependences of the large and the small superconducting gaps measured directly by SnS-Andreev spectroscopy in various Fe-based superconductors and MgB 2 . The experimental ∆ L,S (T ) are well-fitted with a two-gap model based on Moskalenko and Suhl system of equations (supplemented with a BCS-integral renormalization). From the the fitting procedure, we estimate the key attribute of superconducting state -relative electron-boson coupling constants and eigen BCS-ratios for both condensates. Our results evidence for a driving role of a strong intraband coupling in the bands with the large gap, whereas interband coupling is rather weak for all the superconductors under study.

“Break-junction” technique in application to layered superconductors (Review Article)

“…In particular, obtaining similar values for the small gap in experiments on arrays favors of the bulk nature of the order parameter Δ π and the impossibility of interpreting the observed features as manifestation of the surface gap. Note that the maximum values of the large gap Δ σ = 10-11.5 meV that were determined for MgB 2 by us using break-junctions [36,37,[48][49][50][51][52][53] and by the group led by Ekino Δ σ = 9-12 meV [34,37,[48][49][50][51][52][53], coincide. The values of Δ σ were confirmed by that same group using point contact spectroscopy (PCAR) [94].…”

“…This significantly increases the accuracy of determining the superconducting order parameters and the accuracy of the experimental data for two-gap superconductors in comparison to SIS or N(I)S contact spectroscopy, which involve fitting the dynamic conductance by using adjustable parameters [4,5]. Consequently, the temperature dependences of the superconducting gaps are preferably obtained using SnS contacts, which gives us the possibility of accurate estimating the electronphonon (in general, the electron-boson) interaction constant [52,53].…”

“…In our experiments the crystal lattice of the Mg 1−x Al x B 2 samples formally exhibited both insulator and normal metal properties, and SIS and SnS stacks formed on the steps and terraces of the cryogenic clefts due to the layered structure [36,37,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62]. As such, we got the opportunity to apply four types of spectroscopy to the study of the structure of superconducting order parameters, just as we did with cuprates.…”

Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

“…In order to restore strong-coupling constants λ F ull ij , one should add µ * ij , if any, to λ F it ij estimated during the fitting procedure. The latter is detailed in [41,42]. The fits shown by solid lines in Fig.…”

Spin resonance peak in Fe-based superconductors with unequal gaps

“…The latter clearly shows that there are at least two distinct gaps present in 11, 122, and 1111 systems [17][18][19][20][21] and even three gaps in LiFeAs [22,23]. The larger gap ( L ) is about 9 meV and the smaller gap ( S ) is about 4 meV in BaCo122 materials.…”