10,694 research outputs found
Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of - -
Transport and Conductance spectra measurements of ramp-type junctions made of
cuprate superconducting electrodes and a manganite
ferromagnetic barrier are reported. At low
temperatures below , the conductance spectra show Andreev-like broad peaks
superposed on a tunneling-like background, and sometimes also sub-gap Andreev
resonances. The energy gap values found from fits of the data ranged
mostly between 7-10 mV. As usual, the gap features were suppressed under
magnetic fields but revealed the tunneling-like conductance background. After
field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always
higher than under zero field cooling, reflecting the negative magnetoresistance
of the manganite barrier. A signature of superparamagnetism was found in the
conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed
critical currents with barrier thickness of 12 nm or more, were shown to be an
artifact due to incomplete milling of one of the superconducting electrodes.Comment: 10 figure
Andreev reflection in bilayer graphene
We consider the conductance of a normal-superconductor junction in bilayer
graphene in the framework of the Dirac-Bogoliubov-De-Gennes equation. A
remarkable suppression of the conductance at voltages just below the
superconducting gap is found. This can be understood in terms of the spinor
structures of the electron and hole excitations, in particular the reflected
valence band hole being orthogonal to the incoming electron at normal
incidence.
Minor changes in response to referee reports, references updated.Comment: 9 pages, 8 figure
Absorption of heat into a superconductor-normal metal-superconductor junction from a fluctuating environment
We study a diffusive superconductor-normal metal-superconductor junction in
an environment with intrinsic incoherent fluctuations which couple to the
junction through an electromagnetic field. When the temperature of the junction
differs from that of the environment, this coupling leads to an energy transfer
between the two systems, taking the junction out of equilibrium. We describe
this effect in the linear response regime and show that the change in the
supercurrent induced by this coupling leads to qualitative changes in the
current-phase relation and for a certain range of parameters, an increase in
the critical current of the junction. Besides normal metals, similar effects
can be expected also in other conducting weak links.Comment: 5 pages, 4 figures - supplementary information included: 3 pages, 1
figure; minor modifications to the text and Fig. 2, added Ref. 1
Interaction-induced Renormalization of Andreev Reflection
We analyze the charge transport between a one-dimensional weakly interacting
electron gas and a superconductor within the scaling approach in the basis of
scattering states. We derive the renormalization group equations, which fully
account for the intrinsic energy dependence due to Andreev reflection. A strong
renormalization of the corresponding reflection phase is predicted even for a
perfectly transparent metal-superconductor interface. The interaction-induced
suppression of the Andreev conductance is shown to be highly sensitive to the
normal state resistance, providing a possible explanation of experiments with
carbon-nanotube/superconductor junctions by Morpurgo et al. [Science 286, 263
(2001)].Comment: 4 pages, 2 figure
Josephson Currents in Quantum Hall Devices
We consider a simple model for an SNS Josephson junction in which the "normal
metal" is a section of a filling-factor integer quantum-Hall edge. We
provide analytic expressions for the current/phase relations to all orders in
the coupling between the superconductor and the quantum Hall edge modes, and
for all temperatures. Our conclusions are consistent with the earlier
perturbative study by Ma and Zyuzin [Europhysics Letters {\bf 21} 941-945
(1993)]: The Josephson current is independent of the distance between the
superconducting leads, and the upper bound on the maximum Josephson current is
inversely proportional to the perimeter of the Hall device.Comment: Revtex4. 22 pages 9 figures. Replaced version has minor typos fixed
and one added referenc
Simple theory of extremely overdoped HTS
We demonstrate the existence of a simple physical picture of
superconductivity for extremely overdoped CuO2 planes. It possesses all
characteristic features of HTS, such as a high superconducting transition
temperature, the symmetry of order parameter, and the
coexistence of a single electron Fermi surface and a pseudogap in the normal
state. Values of pseudogap are calculated for different doping levels. An
orbital paramagnetism of preformed pairs is predicted.Comment: 7 pages, 1 figur
Effective Lagrangian and Topological Interactions in Supersolids
We construct a low-energy effective Lagrangian describing zero-temperature
supersolids. Galilean invariance imposes strict constraints on the form of the
effective Lagrangian. We identify a topological term in the Lagrangian that
couples superfluid and crystalline modes. For small superfluid fractions this
interaction term is dominant in problems involving defects. As an illustration,
we compute the differential cross section of scatterings of low-energy
transverse elastic phonons by a superfluid vortex. The result is
model-independent.Comment: 10 pages, 1 figure; one reference adde
Unconventional metallic conduction in two-dimensional Hubbard-Wigner lattices
The interplay between long-range and local Coulomb repulsion in strongly
interacting electron systems is explored through a two-dimensional
Hubbard-Wigner model. An unconventional metallic state is found in which
collective low-energy excitations characteristic of the Wigner crystal induce a
flow of electrical current despite the absence of one-electron spectral weight
at the Fermi surface. Photoemission experiments on certain quarter-filled
layered molecular crystals should observe a gap in the excitation spectrum
whereas optical spectroscopy should find a finite Drude weight indicating
metallic behavior.Comment: 10 pages, accepted for publication in PR
Ferromagnetic features on zero-bias conductance peaks in ferromagnet/insulator/superconductor junction
We present a formula for tunneling conductance in ballistic
ferromagnet/ferromagnetic insulator/superconductor junctions where the
superconducting state has opposite spin pairing symmetry. The formula can
involve correctly a ferromagnetism has been induced by effective mass
difference between up- and down-spin electrons. Then, this effective mass
mismatch ferromagnet and standard Stoner ferromagnet have been employed in this
paper. As an application of the formulation, we have studied the tunneling
effect for junctions including spin-triplet p-wave superconductor. The
conductace spectra show a clear difference between two ferromagnets depending
upon the way of normalization of the conductance. Especially, a essential
difference is seen in zero-bias conductance peaks reflecting characteristics of
each ferromagnets. From obtained results, it will be suggested that the
measurements of the tunneling conductance in the junction provide us a useful
information about the mechanism of itinerant ferromagnetism in metal.Comment: 8 pages, 8 figures, references added to the first versio
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