60 research outputs found
Estimation of intraband and interband relative coupling constants from temperature dependences of the order parameter for two-gap superconductors
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. The experimental 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 \textemdash
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.Comment: 7 pages, 5 figures, accepted to J. Supercond. Novel Mag
Evidence of a multiple boson emission in SmThOFeAs
We studied a reproducible fine structure observed in dynamic conductance
spectra of Andreev arrays in SmThOFeAs superconductors with various
thorium concentrations () and critical temperatures \,K. This structure is unambiguously caused by a multiple boson emission
(of the same energy) during the process of multiple Andreev reflections. The
directly determined energy of the bosonic mode reaches \,meV for optimal compound. Within the studied range of , this
energy as well as the large and the small superconducting
gaps, nearly scales with critical temperature with the characteristic ratio
(and ,
correspondingly) resembling the expected energy of spin
resonance and spectral density enhancement in and states,
respectively.Comment: 10 pages, 4 figure
Direct Evidence of Two Superconducting Gaps in FeSeTe: SnS-Andreev Spectroscopy and Lower Critical Field
We present direct measurements of the superconducting order parameter in
nearly optimal FeSeTe single crystals with critical temperature
K. Using intrinsic multiple Andreev reflection effect (IMARE)
spectroscopy and measurements of lower critical field, we directly determined
two superconducting gaps, meV and meV, and their temperature dependences. We show that a two-band
model fits well the experimental data. The estimated electron-boson coupling
constants indicate a strong intraband and a moderate interband interaction
Experimental study of intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions
We report the first observation of the intrinsic multiple Andreev reflections
effect (IMARE) in S-n-S-...-S-arrays (S = superconductor, n = normal metal)
formed by "break-junction" technique in GdO(F)FeAs superconductor (Tc = 48 - 53
K). We show that superconducting gap peculiarities at dI/dV-spectra sharpen
dramatically in the arrays as compared with that in the single-contact spectra;
this enables to improve significantly accuracy of the bulk superconducting
parameters determination. Using IMARE, we determined the large and the small
gap values \Delta_L = 11 +- 1.1 meV and \Delta_S = 2.6 +- 0.4 meV. The
BCS-ratio 2\Delta_L/kTc^{local} = 5.0 - 5.9 > 3.52 (Tc^{local} is the contact
area critical temperature) evidences for a strong electron-boson coupling. The
results obtained agree well with our previous data by Andreev spectroscopy for
single SnS-contacts.Comment: 6 pages, 6 figure
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