11,820 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
On meteor stream spatial structure theory
The classical spatial representation of meteor streams is an elliptical torus with variable cross section. The position of this torus in space is determined by the mean orbit elements that may be obtained directly from observations of individual meteor stream particles when crossed by the Earth. Since the orbits of individual particles of a stream differ from each other, the distance between them on a plane normal to the mean orbit of elliptical torus forms some area, i.e., a cross section. The size and form of these cross sections change with the change of the direction among the mean orbit and are completely defined by the dispersion values of the orbit elements in a stream. An attempt was made to create an analytical method that would permit description of the spatial and time parameters of meteor streams, i.e., the form and size of their cross section, density of incident flux and their variations along the mean orbit and in time. In this case, the stream is considered as a continuous flux rather than a set of individual particles
Stimulated Raman backscattering of laser radiation in deep plasma channels
Stimulated Raman backscattering (RBS) of intense laser radiation confined by
a single-mode plasma channel with a radial variation of plasma frequency
greater than a homogeneous-plasma RBS bandwidth is characterized by a strong
transverse localization of resonantly-driven electron plasma waves (EPW). The
EPW localization reduces the peak growth rate of RBS and increases the
amplification bandwidth. The continuum of non-bound modes of backscattered
radiation shrinks the transverse field profile in a channel and increases the
RBS growth rate. Solution of the initial-value problem shows that an
electromagnetic pulse amplified by the RBS in the single-mode deep plasma
channel has a group velocity higher than in the case of homogeneous-plasma
Raman amplification. Implications to the design of an RBS pulse compressor in a
plasma channel are discussed.Comment: 11 pages, 3 figures; submitted to Physics of Plasma
Normal-Superfluid Interface Scattering For Polarized Fermion Gases
We argue that, for the recent experiments with imbalanced fermion gases, a
temperature difference may occur between the normal (N) and the gapped
superfluid (SF) phase. Using the mean-field formalism, we study particle
scattering off the N-SF interface from the deep BCS to the unitary regime. We
show that the thermal conductivity across the interface drops exponentially
fast with increasing , where is the chemical potential imbalance.
This implies a blocking of thermal equilibration between the N and the SF
phase. We also provide a possible mechanism for the creation of gap
oscillations (FFLO-like states) as seen in recent studies on these systems.Comment: 4 pages, 3 figure
Current-phase relation of the SNS junction in a superconducting loop
We study the current-phase relation of the
superconductor/normal/superconductor (SNS) junction imbedded in a
superconducting loop. Considering the current conservation and free energy
minimum conditions, we obtain the persistent currents of the
normal/superconductor (NS) loop. At finite temperature we can explain the
experimentally observed highly non-sinusoidal currents which have maxima near
the zero external flux.Comment: 7 pages, 3 figures, version to appear in Europhys. Let
Full counting statistics of a charge pump in the Coulomb blockade regime
We study the full charge counting statistics of a charge pump based on a
nearly open single electron transistor. The problem is mapped onto an exactly
soluble problem of a g=1/2 non-equilibrium Luttinger liquid with an impurity.
We obtain an analytic expression for the generating function of the transmitted
charge for an arbitrary pumping strength. Even though this model contains
fractionally charged excitations only integer transmitted charges can be
observed during finite observation times.Comment: 4 pages, 1 figur
The quadrupolar phases of the S=1 bilinear-biquadratic Heisenberg model on the triangular lattice
Using mean-field theory, exact diagonalizations and SU(3) flavour theory, we
have precisely mapped out the phase diagram of the S=1 bilinear-biquadratic
Heisenberg model on the triangular lattice in a magnetic field, with emphasis
on the quadrupolar phases and their excitations. In particular, we show that
ferroquadrupolar order can coexist with short-range helical magnetic order, and
that the antiferroquadrupolar phase is characterized by a remarkable 2/3
magnetization plateau, in which one site per triangle retains quadrupolar order
while the other two are polarized along the field. Implications for actual S=1
magnets are discussed.Comment: 4 pages, 5 figures, published versio
The effect of Dzyaloshinskii-Moriya interactions on the phase diagram and magnetic excitations of SrCu2(BO3)2
The orthogonal dimer structure in the SrCu2(BO3)2 spin-1/2 magnet provides a
realization of the Shastry-Sutherland model. Using a dimer-product variational
wave function, we map out the phase diagram of the Shastry-Sutherland model
including anisotropies. Based on the variational solution, we construct a
bond-wave approach to obtain the excitation spectra as a function of magnetic
field. The characteristic features of the experimentally measured neutron and
ESR spectra are reproduced, like the anisotropy induced zero field splittings
and the persistent gap at higher fields.Comment: 20 pages,15 figure
Andreev tunneling through a double quantum-dot system coupled to a ferromagnet and a superconductor: effects of mean field electronic correlations
We study the transport properties of a hybrid nanostructure composed of a
ferromagnet, two quantum dots, and a superconductor connected in series. By
using the non-equilibrium Green's function approach, we have calculated the
electric current, the differential conductance and the transmittance for
energies within the superconductor gap. In this regime, the mechanism of charge
transmission is the Andreev reflection, which allows for a control of the
current through the ferromagnet polarization. We have also included interdot
and intradot interactions, and have analyzed their influence through a mean
field approximation. In the presence of interactions, Coulomb blockade tend to
localized the electrons at the double-dot system, leading to an asymmetric
pattern for the density of states at the dots, and thus reducing the
transmission probability through the device. In particular, for non-zero
polarization, the intradot interaction splits the spin degeneracy, reducing the
maximum value of the current due to different spin-up and spin-down densities
of states. Negative differential conductance (NDC) appears for some regions of
the voltage bias, as a result of the interplay of the Andreev scattering with
electronic correlations. By applying a gate voltage at the dots, one can tune
the effect, changing the voltage region where this novel phenomenon appears.
This mechanism to control the current may be of importance in technological
applications.Comment: 12 pages, 11 figure
Semiclassical Approach to Competing Orders in Two-leg Spin Ladder with Ring-Exchange
We investigate the competition between different orders in the two-leg spin
ladder with a ring-exchange interaction by means of a bosonic approach. The
latter is defined in terms of spin-1 hardcore bosons which treat the N\'eel and
vector chirality order parameters on an equal footing. A semiclassical approach
of the resulting model describes the phases of the two-leg spin ladder with a
ring-exchange. In particular, we derive the low-energy effective actions which
govern the physical properties of the rung-singlet and dominant vector
chirality phases. As a by-product of our approach, we reveal the mutual
induction phenomenon between spin and chirality with, for instance, the
emergence of a vector-chirality phase from the application of a magnetic field
in bilayer systems coupled by four-spin exchange interactions.Comment: 15 pages, 9 figure
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