160 research outputs found
Antiferromagnetic order and dielectric gap within the vortex core of antiferromagnetic superconductor
The structure of a superconducting vortex has been studied theoretically for
a dirty antiferromagnetic superconductor (AFSC), modelling an AFSC as a doped
semi-metal with s-wave superconducting pairing and antiferromagnetic
(dielectric) interaction between electrons (holes). It is also supposed that
the quasiparticles dispersion law possesses the property of nesting. The
distribution of the superconducting and magnetic order parameters near the
vortex core is calculated. It is shown that the antiferromagnetic order, been
suppressed at large distances, is restored around the superconducting flux and
the vortex core is in fact insulating and antiferromagnetic, in stark contrast
to the normal metal cores of traditional superconductors. Moreover, our model
calculations predict that as the temperature decreases the flux region of the
superconductivity and antiferromagnetism coexistence increases.Comment: 9 pages, 3 Postscript figures,NATO Advanced Research Workshop on
"Vortex dynamics in superconductors and other complex systems" Yalta, Crimea,
Ukraine, 13-17 September 200
Enhancement of the Josephson current by magnetic field in superconducting tunnel structures with paramagnetic spacer
The dc Josephson critical current of a (S/M)IS tunnel structure in a parallel
magnetic field has been investigated (here S is a superconductor, S/M is the
proximity coupled S and paramagnet M bilayer and I is an insulating barrier).
We consider the case when, due to the Hund's rule, in the M metal the effective
molecular interaction aligns spins of the conducting electrons antiparallel to
localized spins of magnetic ions. It is predicted that for tunnel structures
under consideration there are the conditions when the destructive action of the
internal and the applied magnetic fields on Cooper pairs is weakened and the
increase of the applied magnetic field causes the field-induced enhancement of
the tunnel critical current. The experimental realization of this interesting
effect of the interplay between superconductivity and magnetism is also
discussed.Comment: 5 pages 3 figure
The influence of various factors on recovery process of motor control of paretic limbs muscles in patients with pyramidal syndrome
In order to study the specific features of central nervous system reaction to restoration of the cranial vault bone defects by distraction, osteosynthesis method, the electroneuromyographic examination was performed in 28 patients of 16—62 years (average age — 40,1 ± 2,6 years) with pyramidal syndrome in late recovery or residual period, of the disease (severe brain injury cerebral stroke). The main trends in electroneuromyographic indice — "cerebrospinal index" — in patients during the replacement process of post-traumatic or simulated cranial vault bone defects using transosseous distraction osteosynthesis were analyzed. The specific features of the central nervous system responses to surgical treatment, age, etiology, the brain structures initial lesion severity and disease duration were studied. As the results of the research it was established that replacement of defects of calvarium bones by transosseous distraction osteosynthesis in patients with consequences of craniocerebral trauma or stroke had. more intensive positive influence on motor zones of cerebral cortex, that shows itself in increase of effectiveness of motor control, in middle age people, at traumatic etiology of disease, at moderate pyramidal insufficiency and. at remoteness of the disease up to 1 year. Obtained data is expedient to take into account at primary selection of patients for operative treatment
BILATERAL INTERRELATIONS OF ENMGAND EEG-CHARACTERISTICS OF PYRAMID INSUFFICIENCY IN PATIENTS WITH THE CONSEQUENCES OF STROKE AND OF BRAIN INJURY
The aim. of the work was to estimate the degree of intensity of interhemispheric interaction with use of complex neurophysiological (electroneuromyography, electroencephalography) testing of 163 patients of 12—74 years in residual period, of ischemic (n = 108) and hemorrhagic (n = 22) hemispheric stroke and. severe craniocerebral injury with brain contusion (n = 33). Obtained, data testifies to the distinct negative influence of postinsult/ posttraumatic cerebral defect on functional characteristica of counter-lateral ("intact") hemisphere that is reflected in proportional changes of all the spectrum, of analyzed, neurophysiological signs. These changes affects all the tested, modules of neuromotor system, and. can be observed over a long period, after the stroke or craniocerebral injury
Layered ferromagnet-superconductor structures: the state and proximity effects
We investigate clean mutilayered structures of the SFS and SFSFS type, (where
the S layer is intrinsically superconducting and the F layer is ferromagnetic)
through numerical solution of the self-consistent Bogoliubov-de Gennes
equations for these systems. We obtain results for the pair amplitude, the
local density of states, and the local magnetic moment. We find that as a
function of the thickness of the magnetic layers separating adjacent
superconductors, the ground state energy varies periodically between two stable
states. The first state is an ordinary "0-state", in which the order parameter
has a phase difference of zero between consecutive S layers, and the second is
a "-state", where the sign alternates, corresponding to a phase difference
of between adjacent S layers. This behavior can be understood from simple
arguments. The density of states and the local magnetic moment reflect also
this periodicity.Comment: 12 pages, 10 Figure
Inhomogeneous magnetism induced in a superconductor at superconductor-ferromagnet interface
We study a magnetic proximity effect at superconductor (S) - ferromagnet (F)
interface. It is shown that due to an exchange of electrons between the F and S
metals ferromagnetic correlations extend into the superconductor, being
dependent on interface parameters. We show that ferromagnetic exchange field
pair breaking effect leads to a formation of subgap bands in the S layer local
density of states, that accommodate only one spin-polarized quasiparticles.
Equilibrium magnetization leakage into the S layer as function of SF interface
quality and a value of ferromagnetic interaction have also been calculated. We
show that a damped-oscillatory behavior versus distance from SF interface is a
distinguished feature of the exchange-induced magnetization of the S layer.Comment: 10 pages, 7 Postscript figure
Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles
The thermal behavior of free and alumina-supported iron-carbon nanoparticles
is investigated via molecular dynamics simulations, in which the effect of the
substrate is treated with a simple Morse potential fitted to ab initio data. We
observe that the presence of the substrate raises the melting temperature of
medium and large nanoparticles ( = 0-0.16, = 80-1000, non-
magic numbers) by 40-60 K; it also plays an important role in defining the
ground state of smaller Fe nanoparticles ( = 50-80). The main focus of our
study is the investigation of Fe-C phase diagrams as a function of the
nanoparticle size. We find that as the cluster size decreases in the
1.1-1.6-nm-diameter range the eutectic point shifts significantly not only
toward lower temperatures, as expected from the Gibbs-Thomson law, but also
toward lower concentrations of C. The strong dependence of the maximum C
solubility on the Fe-C cluster size may have important implications for the
catalytic growth of carbon nanotubes by chemical vapor deposition.Comment: 13 pages, 11 figures, higher quality figures can be seen in article 9
at http://alpha.mems.duke.edu/wahyu
Feasibility of study magnetic proximity effects in bilayer "superconductor/ferromagnet" using waveguide-enhanced Polarized Neutron Reflectometry
A resonant enhancement of the neutron standing waves is proposed to use in
order to increase the magnetic neutron scattering from a
"superconductor/ferromagnet"(S/F) bilayer. The model calculations show that
usage of this effect allows to increase the magnetic scattering intensity by
factor of hundreds. Aspects related to the growth procedure (order of
deposition, roughness of the layers etc) as well as experimental conditions
(resolution, polarization of the neutron beam, background etc) are also
discussed.
Collected experimental data for the S/F heterostructure
Cu(32nm)/V(40nm)/Fe(1nm)/MgO confirmed the presence of a resonant 60-fold
amplification of the magnetic scattering.Comment: The manuscript of the article submitted to Crysstalography Reports.
23 pages, 5 figure
Josephson effect in double-barrier superconductor-ferromagnet junctions
We study the Josephson effect in ballistic double-barrier SIFIS planar
junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet
(F), and insulating interfaces (I). We solve the scattering problem based on
the Bogoliubov--de Gennes equations and derive a general expression for the dc
Josephson current, valid for arbitrary interfacial transparency and Fermi wave
vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle
transmission resonances contribute significantly to the Andreev process. The
Josephson current is calculated for various parameters of the junction, and the
influence of both interfacial transparency and FWVM is analyzed. For thin
layers of strong ferromagnet and finite interfacial transparency, we find that
coherent (geometrical) oscillations of the maximum Josephson current are
superimposed on the oscillations related to the crossover between 0 and
states. For the same case we find that the temperature-induced
transition occurs if the junction is very close to the crossovers at zero
temperature.Comment: 13 pages, 6 figure
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