125 research outputs found
Point-Contact Spectroscopy on RuSr2GdCu2O8
We present Point-Contact experiments on polycrystalline RuSrGdCuO
samples. The majority of tunneling curves shows a zero-bias conductance peak,
which is modeled by assuming a d-wave pairing symmetry of the superconducting
order parameter.The magnetic field dependence of the conductance spectra has
been measured in very stable junctions. In some cases, due to the granularity
of the samples, clusters of grains in series introduce peculiar features in the
conductance spectra.Comment: 4 pages, 4 figures, published on Journal of Physics and Chemistry of
Solid
Point Contact Study of the Superconducting Order Parameter in RuSr2GdCu2O8
We have performed a detailed study of the conductance characteristics
obtained by point contact junctions realized between a normal Pt/Ir tip and
syntered RuSr2GdCu2O8 (Ru-1212) samples. Indeed, this compound is subject of
great interest due to the coexistence of both magnetic order and bulk
superconductivity. In our experiments, the low temperature tunneling spectra
reproducibly show a zero bias conductance peak that can be well reproduced by a
generalized BTK model in the case of d-wave symmetry of the superconducting
order parameter.Comment: 3 pages, 2 figures, IJMPB style. Presented at New3SC5 Conference,
China, June 200
Subharmonic gap structures and Josephson effect in MgB2/Nb micro-constrictions
Superconducting micro-constrictions between Nb tips and high quality
MgB pellets have been realized by means of a point-contact inset, driven
by a micrometric screw. Measurements of the current-voltage characteristics and
of the dynamical conductance versus bias have been performed in the temperature
range between 4.2 K and 500 K. Above the Nb critical temperature T,
the conductance of the MgB/normal-metal constrictions behaves as predicted
by the BTK model for low resistance contacts while high resistance junctions
show quasiparticle tunneling characteristics. Consistently, from the whole set
of data we infer the value meV for the
three-dimensional gap of MgB. Below T, low resistance contacts
show Josephson current and subharmonic gap structures (SGS), due to multiple
Andreev reflections. Simultaneous observations of both features, unambiguously
indicate coupling of the 3D band of MgB with the Nb superconducting order
parameter. We found that the temperature dependence of the Josephson critical
current follows the classical Ambegaokar-Baratoff behavior with a value
meV at low temperatures.Comment: 8 pages, 5 figures. Replaced with published versio
Pairing state in the rutheno-cuprate superconductor RuSr2GdCu2O8: A point contact Andreev Reflection Spectroscopy study
The results of Point Contact Andreev Reflection
Spectroscopy on polycrystalline RuSrGdCuO pellets are presented.
The wide variety of the measured spectra are all explained in terms of a
modified BTK model considering a \emph{d-wave} symmetry of the superconducting
order parameter. Remarkably low values of the energy gap and of the ratio are inferred. From the
temperature evolution of the vs characteristics we extract a
sublinear temperature dependence of the superconducting energy gap. The
magnetic field dependence of the conductance spectra at low temperatures is
also reported. From the vs evolution, a critical magnetic field
is inferred. To properly explain the curves showing
gap-like features at higher voltages, we consider the formation of a Josephson
junction in series with the Point Contact junction, as a consequence of the
granularity of the sample.Comment: 8 pages, 7 EPS figures. Accepted in Phys. Rev.
Point Contact Spectra on YBaCuO/LaCaMnO bilayers
We present conductance characteristics of point contact junctions realized
between a normal Pt-Ir tip and
YBaCuO/LaCaMnO (YBCO/LCMO) bilayers. The
point contact characteristics show a zero bias conductance peak, as a
consequence of the formation of Andreev bound states at the YBCO Fermi level.
The temperature evolution of the spectra reveals a depressed zero bias peak and
a reduced superconducting energy gap, both explainable in terms of spin
polarization effects due to the LCMO layer.Comment: 4 pages, 4 EPS figures. Proceedings of EUCAS 2005. Accepted in
Journal of Physics: Conference Serie
Generalized Blonder-Tinkham-Klapwijk theory and conductance spectra with particle-hole mixing interface potential
We extend the Blonder-Tinkham-Klapwijk treatment including particle-hole mixing boundary conditions in the Bogoliubov-de Gennes scattering problem to describe anomalous conductance features often reported in normal-metal/superconductor junctions. We calculate the differential conductance spectra and show that conductance dips, not expected in the standard formulation, can be explained in terms of a phase π-shift between the bulk and the interface order parameter. A tight-binding model is also introduced to give a quantitative description of the phase-shift in terms of the transparency and polarization of the interface. We characterize the physics arising from particle-hole mixing boundary conditions at the interface and its effects on the conductance anomalies in superconductor-normal heterostructures
Charge transfer and trapping as origin of a double dip in the transfer characteristics of graphene based field-effect transistors
We discuss the origin of an additional dip other than the charge neutrality
point observed in transfer characteristics of graphene-based field-effect
transistors. The double-dip is proved to arise from charge transfer between
graphene and metal electrodes, while charge storage at the graphene/SiO2
interface enhances it. Considering different Fermi energy from the neutrality
point along the channel and partial charge pinning at the contacts, we propose
a model which explains all features in gate voltage loops.Comment: 14 pages, 5 figure
Andreev reflection in ferrimagnetic CoFe2O4/SrRuO3 spin filters
We have performed point contact spectroscopy measurements on a sample
constituted by a metallic ferromagnetic oxide (SrRuO_3) bottom electrode and a
tunnel ferrimagnetic (CoFe_2O_4) barrier. Andreev reflection is observed across
the tunnel barrier. From the comparison of Andreev reflection in SrRuO3 and
across the CoFe_2O_4 barrier we infer that the ferrimagnetic barrier has a spin
filter efficiency not larger than +13%. The observation of a moderate and
positive spin filtering is discussed in the context of the microstructure of
the barriers and symmetry-related spin filtering effects.Comment: 13 pages, 5 figures. To appear in Phys. Rev. B
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