762 research outputs found
Competitive 0 and {\pi} states in S/F multilayers: multimode approach
We have investigated the critical temperature behavior in periodic
superconductor/ ferromagnet (S/F) multilayers as a function of the
ferromagnetic layer thickness and the interface transparency. The
critical temperature exhibits a damped oscillatory behavior in these
systems due to an exchange field in the ferromagnetic material. In this work we
have performed calculations using the self-consistent multimode approach,
which is considered to be exact solving method. Using this approach we have
derived the conditions of 0 or state realization in periodic S/F
multilayers. Moreover, we have presented the comparison between the single-mode
and multimode approaches and established the limits of applicability of the
single-mode approximation, frequently used by experimentalists
Antiferromagnetic resonances in superconductor-ferromagnet multilayers
In this work, we study magnetization dynamics in superconductor-ferromagnet
(S-F) thin-film multilayer. Theoretical considerations supported by the
broad-band ferromagnetic resonance spectroscopy reveal development of acoustic
and optic resonance modes in S-F multilayers at significantly higher
frequencies in comparison to the Kittel mode of individual F-layers. These
modes are formed due to antiferromagnetic-like interaction between F-layers via
shared circulating superconducting currents in S-layers. The gap between
resonance modes is determined by the thickness and superconducting penetration
depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability
opens wide prospects for application of these multialyers in magnonics as well
as in various superconducting hybrid systems.Comment: 5 pages, 4 figures, 34 reference
Tight inequalities for nonclassicality of measurement statistics
In quantum optics, measurement statistics -- for example, photocounting
statistics -- are considered nonclassical if they cannot be reproduced with
statistical mixtures of classical radiation fields. We have formulated a
necessary and sufficient condition for such nonclassicality. This condition is
given by a set of inequalities that tightly bound the convex set of
probabilities associated with classical electromagnetic radiation. Analytical
forms for full sets and subsets of these inequalities are obtained for
important cases of realistic photocounting measurements and unbalanced homodyne
detection. As an example, we consider photocounting statistics of
phase-squeezed coherent states. Contrary to a common intuition, the analysis
developed here reveals distinct nonclassical properties of these statistics
that can be experimentally corroborated with minimal resources.Comment: 12 pages, 4 figure
Influence of Sintering Conditions on Specific Electrical Conductivity in Aluminum-Graphene Composite
Dependence of specific electrical resistance on temperature (20 - 1600 ∘C) and processing method in an aluminum-graphene (up to 2wt.%) composite is investigated. It is established that spark plasma sintering (SPS) under pressure 40 MPа does not influence on electrical resistance, whereas SPS at low pressure (<10 MPa) reduces electrical resistance at a room temperature on 6 orders. Lower values of electrical resistance (up to 90 Ω *mm) received at sintering in hot pressing set at radiating heating. It is supposed that the reason of sharp decrease in electrical resistance at the lowered pressure is presence of current pulsations during SPS. They induces magnetic fields in graphene flake which lead to their moving and forming of particles to electroconductive chains or their capture in arched cells at applied pressure.
Keywords: composite, aluminum, graphene, electrical resistance, temperature dependence
Foreground separation using a flexible maximum-entropy algorithm: an application to COBE data
A flexible maximum-entropy component separation algorithm is presented that
accommodates anisotropic noise, incomplete sky-coverage and uncertainties in
the spectral parameters of foregrounds. The capabilities of the method are
determined by first applying it to simulated spherical microwave data sets
emulating the COBE-DMR, COBE-DIRBE and Haslam surveys. Using these simulations
we find that is very difficult to determine unambiguously the spectral
parameters of the galactic components for this data set due to their high level
of noise. Nevertheless, we show that is possible to find a robust CMB
reconstruction, especially at the high galactic latitude. The method is then
applied to these real data sets to obtain reconstructions of the CMB component
and galactic foreground emission over the whole sky. The best reconstructions
are found for values of the spectral parameters: T_d=19 K, alpha_d=2,
beta_ff=-0.19 and beta_syn=-0.8. The CMB map has been recovered with an
estimated statistical error of \sim 22 muK on an angular scale of 7 degrees
outside the galactic cut whereas the low galactic latitude region presents
contamination from the foreground emissions.Comment: 29 pages, 25 figures, version accepted for publication in MNRAS. One
subsection and 6 figures added. Main results unchange
Reentrant superconductivity in proximity to a topological insulator
In the following paper we investigate the critical temperature behavior
in the two-dimensional S/TI (S denotes superconductor and TI - topological
insulator) junction with a proximity induced in-plane helical magnetization in
the TI surface. The calculations of are performed using the general
self-consistent approach based on the Usadel equations in Matsubara Green's
functions technique. We show that the presence of the helical magnetization
leads to the nonmonotonic behavior of the critical temperature as a function of
the topological insulator layer thickness.Comment: submitted to Physical Review
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