6,611 research outputs found
Andreev reflections on Y1-xCaxBa2Cu3O7-delta evidence for an unusual proximity effect
We have measured Andreev reflections between an Au tip and
Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7 - \delta} thin films in the in-plane orientation.
The conductance spectra are best fitted with a pair potential having the
"d_{x^{2}-y^{2}+is" symmetry. We find that the amplitude of the "is" component
is enhanced as the contact transparency is increased. This is an indication for
an unusual proximity effect that modifies the pair potential in the
superconductor near the surface with the normal metal.Comment: 4 pages, 4 figure
Triple-gap superconductivity of MgB2 - (La,Sr)MnO3 composite. Which of the gaps is proximity induced?
Interplay of superconductivity and magnetism in a composite prepared of the
ferromagnetic half-metallic La_0.67Sr_0.33MnO (LSMO) nanoparticles and the
conventional s-wave superconductor MgB_2 has been studied. A few principal
effects have been found in bulk samples. With an onset of the MgB_2
superconductivity, a spectacular drop of the sample resistance has been
detected and superconductivity has been observed at temperature up to 20K.
Point-contact (PC) spectroscopy has been used to measure directly the
superconducting energy coupling. For small voltage, an excess current and
doubling of the PC's normal state conductance have been found. Conductance
peaks corresponding to three energy gaps are clearly observed. Two of these
gaps we identified as enhanced \Delta_{\pi} and \Delta_{\sigma} gaps
originating from the MgB_2; the third gap \Delta_{tr} is more than three times
larger than the largest MgB_2 gap. The experimental results provide unambiguous
evidences for a new type of proximity effect which follows the phase coherency
scenario of proximity induced superconductivity. Specifically, at low
temperature, the p-wave spin-triplet condensate with pairing energy \Delta_{tr}
is essentially sustained in LSMO but is incapable to display long-range
supercurrent response because of a phase-disordering state. The proximity
coupling to MgB_2 restores the long-range phase coherency of the triplet
superconducting state, which, in turn, enhances superconducting state of the
MgB_2.Comment: 10 pages, 6 figure
Coexistence of a triplet nodal order-parameter and a singlet order-parameter at the interfaces of ferromagnet-superconductor Co/CoO/In junctions
We present differential conductance measurements of Cobalt / Cobalt-Oxide /
Indium planar junctions, 500nm x 500nm in size. The junctions span a wide range
of barriers, from very low to a tunnel barrier. The characteristic conductance
of all the junctions show a V-shape structure at low bias instead of the
U-shape characteristic of a s-wave order parameter. The bias of the conductance
peaks is, for all junctions, larger than the gap of indium. Both properties
exclude pure s-wave pairing. The data is well fitted by a model that assumes
the coexistence of s-wave singlet and equal spin p-wave triplet fluids. We find
that the values of the s-wave and p-wave gaps follow the BCS temperature
dependance and that the amplitude of the s-wave fluid increases with the
barrier strength.Comment: 5 pages, Accepted to Phys. Rev.
Conductance characteristics between a normal metal and a two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov superconductor: the Fulde-Ferrell state
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has received renewed
interest recently due to the experimental indication of its presence in
CeCoIn, a quasi 2-dimensional (2D) d-wave superconductor. However direct
evidence of the spatial variation of the superconducting order parameter, which
is the hallmark of the FFLO state, does not yet exist. In this work we explore
the possibility of detecting the phase structure of the order parameter
directly using conductance spectroscopy through micro-constrictions, which
probes the phase sensitive surface Andreev bound states of d-wave
superconductors. We employ the Blonder-Tinkham-Klapwijk formalism to calculate
the conductance characteristics between a normal metal (N) and a 2D - or
-wave superconductor in the Fulde-Ferrell state, for all barrier
parameter from the point contact limit () to the tunneling limit (). We find that the zero-bias conductance peak due to these surface
Andreev bound states observed in the uniform d-wave superconductor is split and
shifted in the Fulde-Ferrell state. We also clarify what weighted bulk density
of states is measured by the conductance in the limit of large .Comment: 10 pages, 13 figure
Multifrequency dial sensing of the atmospheric gaseous constituents using the first and second harmonics of a tunable CO2 laser radiation
The results of field measurements of concentration of some gaseous components of the atmosphere along the paths, in Sofia, Bulgaria, using a gas analyzer based on the use of a CO2 laser radiation frequency-doubled with ZnGeP2 monocrystals are presented. The gas analyzer is a traditional long path absorption meter. Radiation from the tunable CO2 laser of low pressure and from an additional He-Ne laser is directed to a colliminating hundredfold Gregori telescope with a 300 mm diameter of the principal mirror. The dimensions of the mirrors of a retroreflector 500 x 500 mm and a receiving telescope allow one to totally intercept the beam passed through the atmospheric layer under study and back
Non-Fraunhofer patterns of the anharmonic Josephson current influenced by a strong interfacial pair breaking
In the junctions with a strong Josephson coupling and a pronounced
interfacial pair breaking, the magnetic interference patterns of the Josephson
current are shown to differ substantially from the standard Fraunhofer shape.
The Fraunhofer pattern occurs, when Josephson couplings are weak. The narrow
peak of the critical current, centered at the zero magnetic field, and the
suppressed hills at finite field values are the characteristic features of the
non-Fraunhofer magnetic field modulation of the critical current, obtained in
this paper.Comment: 5 pages, 4 figure
Multiband superconductivity in the heavy fermion compound PrOs4Sb12
The thermal conductivity of the heavy fermion superconductor PrOs4Sb12 was
measured down to Tc/40 throughout the vortex state. At lowest temperatures and
for magnetic fields H ~ 0.07Hc2, already 40% of the normal state thermal
conductivity is restored. This behaviour (similar to that observed in MgB2) is
a clear signature of multiband superconductivity in this compound.Comment: 12pages, version #1 20\_06\_200
Andreev Reflection in Strong Magnetic Fields
We have studied the interplay of Andreev reflection and cyclotron motion of
quasiparticles at a superconductor-normal-metal interface with a strong
magnetic field applied parallel to the interface. Bound states are formed due
to the confinement introduced both by the external magnetic field and the
superconducting gap. These bound states are a coherent superposition of
electron and hole edge excitations similar to those realized in finite
quantum-Hall samples. We find the energy spectrum for these Andreev edge states
and calculate transport properties.Comment: 5 pages, 3 figures, RevTex, revised to include more detailed
discussion of currents and transpor
Andreev experiments on superconductor/ferromagnet point contacts
Andreev reflection is a smart tool to investigate the spin polarisation P of
the current through point contacts between a superconductor and a ferromagnet.
We compare different models to extract P from experimental data and investigate
the dependence of P on different contact parameters.Comment: 14 pages, 5 figures, accepted for publication in Fizika Nizkikh
Temperatu
Phase Dependent Thermopower in Andreev Interferometers
We report measurements of the thermopower S of mesoscopic Andreev
interferometers, which are hybrid loops with one arm fabricated from a
superconductor (Al), and one arm from a normal metal (Au). S depends on the
phase of electrons in the interferometer, oscillating as a function of magnetic
flux with a period of one flux quantum (= h/2e). The magnitude of S increases
as the temperature T is lowered, reaching a maximum around T = 0.14 K, and
decreases at lower temperatures. The symmetry of S oscillations with respect to
magnetic flux depends on the topology of the sample.Comment: 4 pages, 4 figure
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