304 research outputs found
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
Superconducting properties of sulfur-doped iron selenide
The recent discovery of high-temperature superconductivity in single-layer
iron selenide has generated significant experimental interest for optimizing
the superconducting properties of iron-based superconductors through the
lattice modification. For simulating the similar effect by changing the
chemical composition due to S doping, we investigate the superconducting
properties of high-quality single crystals of FeSeS (=0, 0.04,
0.09, and 0.11) using magnetization, resistivity, the London penetration depth,
and low temperature specific heat measurements. We show that the introduction
of S to FeSe enhances the superconducting transition temperature ,
anisotropy, upper critical field , and critical current density
. The upper critical field and its anisotropy are strongly
temperature dependent, indicating a multiband superconductivity in this system.
Through the measurements and analysis of the London penetration depth and specific heat, we show clear evidence for strong coupling two-gap
-wave superconductivity. The temperature-dependence of
calculated from the lower critical field and electronic specific heat can be
well described by using a two-band model with -wave-like gaps. We find that
a -wave and single-gap BCS theory under the weak-coupling approach can not
describe our experiments. The change of specific heat induced by the magnetic
field can be understood only in terms of multiband superconductivity.Comment: 13 pages, 7 figure
Quasi Two-dimensional Vortex Matter in ThH Superhydride
A comprehensive study of the vortex phases and vortex dynamics is presented
for a recently discovered high-temperature superconductor ThH with
= 153 K at 170 GPa. The obtained results strongly suggest a
quasi two-dimensional (2D) character of the vortex glass phase transition in
ThH. The activation energy yields a logarithmic dependence
ln() on magnetic field in a low field
region and a power law dependence ~ in a
high field region, signaling a crossover from 2D regime to 3D collective
pinning regime, respectively. Additionally, a pinning force field dependence
showcases dominance of surface-type pinning in the vicinity of
. Thermal activation energy (), derived within
thermally activated flux flow (TAFF) theory, takes very high values above
210 K together with the Ginzburg number = 0.039 -
0.085, which is lower only than those of BiSrCaCuO cuprates and 10-3-8 family
of iron based superconductor. This indicates the enormous role of thermal
fluctuations in the dynamics of the vortex lattice of superhydrides, the
physics of which is similar to the physics of unconventional high-temperature
superconductors
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