114 research outputs found
Investigation of LiFeAs by means of "Break-junction" Technique
In our tunneling investigation using Andreev superconductor - normal metal -
superconductor contacts on LiFeAs single crystals we observed two reproducible
independent subharmonic gap structures at dynamic conductance characteristics.
From these results, we can derive the energy of the large superconducting gap
meV and the small gap meV at
K for the K (the contact area
critical temperature which deviation causes the variation of ). The
BCS-ratio is found to be , whereas
results from induced superconductivity in the bands
with the small gap.Comment: 7 pages, 5 figures. Published in Pis'ma v ZhETF 95, 604-610 (2012
Study of the Two-Gap Superconductivity in GdO(F)FeAs by ScS-Andreev Spectroscopy
Current-voltage characteristics and dynamic conductance of the superconductor
- constriction - superconductor junctions in GdO(F)FeAs polycrystalline samples
with critical temperatures Tc^local = 46 - 53 K were investigated. Two
superconducting gaps, the large Delta_L = 10.5 +- 2 meV, and the small one
Delta_S = 2.3 +- 0.4 meV were clearly observed at T = 4.2 K. The
2Delta_L/kTc^local = 5.5 +- 1 ratio gives support to the strong coupling
mechanism which is responsible for the high Tc value. Temperature dependence of
the large gap Delta_L(T) indicates the presence of intrinsic proximity effect
(in k-space) between two superconducting condensates.Comment: 7 pages, 6 figures. Submitted to Journal of Physics: Conference
Serie
Angular distributions of scattered excited muonic hydrogen atoms
Differential cross sections of the Coulomb deexcitation in the collisions of
excited muonic hydrogen with the hydrogen atom have been studied for the first
time. In the framework of the fully quantum-mechanical close-coupling approach
both the differential cross sections for the transitions and
-averaged differential cross sections have been calculated for exotic atom
in the initial states with the principle quantum number at relative
motion energies eV and at scattering angles
. The vacuum polarization shifts of the
-states are taken into account. The calculated in the same approach
differential cross sections of the elastic and Stark scattering are also
presented. The main features of the calculated differential cross sections are
discussed and a strong anisotropy of cross sections for the Coulomb
deexcitation is predicted.Comment: 5 pages, 9 figure
Decay of Quasi-Particle in a Quantum Dot: the role of Energy Resolution
The disintegration of quasiparticle in a quantum dot due to the electron
interaction is considered. It was predicted recently that above the energy
\eps^{*} = \Delta(g/\ln g)^{1/2} each one particle peak in the spectrum is
split into many components ( and are the one particle level spacing
and conductance). We show that the observed value of \eps^{*} should depend
on the experimental resolution \delta \eps. In the broad region of variation
of \delta \eps the should be replaced by \ln(\Delta/ g\delta \eps).
We also give the arguments against the delocalization transition in the Fock
space. Most likely the number of satellite peaks grows continuously with
energy, being at \eps \sim \eps^{*}, but remains finite at \eps >
\eps^{*}. The predicted logarithmic distribution of inter-peak spacings may be
used for experimental confirmation of the below-Golden-Rule decay.Comment: 5 pages, REVTEX, 2 eps figures, version accepted for publication in
Phys. Rev. Let
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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