1,812,847 research outputs found
Long range triplet Josephson effect through a ferromagnetic trilayer
We study the Josephson current through a ferromagnetic trilayer, both in the
diffusive and clean limits. For colinear (parallel or antiparallel)
magnetizations in the layers, the Josephson current is small due to short range
proximity effect in superconductor/ferromagnet structures. For non colinear
magnetizations, we determine the conditions for the Josephson current to be
dominated by another contribution originating from long range triplet proximity
effect.Comment: 4 pages, 2 figure
Triplet contribution to the Josephson current in the nonequilibrium superconductor/ferromagnet/superconductor junction
The Josephson current through a long s-wave superconductor/weak
ferromagnet/s-wave superconductor weak link is studied theoretically in the
regime of nonequilibrium spin-dependent occupation of electron states in the
ferromagnetic intelayer. While under the considered nonequilibrium condition
the standard supercurrent, carried by the singlet part of current-carrying
density of states, is not modified, the additional supercurrent flowing via the
triplet part of the current-carrying density of states appears. Depending on
voltage, controlling the particular form of spin-dependent nonequilibrium in
the interlayer, this additional current can enhance or reduce the usual current
of the singlet component and also switch the junction between 0- and
-states.Comment: 4 pages, 1 figur
Influence of the spin-dependent quasiparticle distribution on the Josephson current through a ferromagnetic weak link
The Josephson current flowing through weak links containing ferromagnetic
elements is studied theoretically under the condition that the quasiparticle
distribution over energy states in the interlayer is spin-dependent. It is
shown that the interplay between the spin-dependent quasiparticle distribution
and the triplet superconducting correlations induced by the proximity effect
between the superconducting leads and ferromagnetic elements of the interlayer,
leads to the appearence of an additional contribution to the Josephson current.
This additional contribution can be extracted from the full Josephson
current in experiment. The features of the additional supercurrent , which
are of main physical interest are the following: (i) We propose the
experimental setup, where the contributions given by the short-range (SRTC) and
long-range (LRTC) components of triplet superconducting correlations in the
interlayer can be measured separately. It can be realized on the basis of
S/N/F/N/S junction, where the interlayer is composed of two normal metal
regions with a spiral ferromagnet layer sandwiched between them. For the case
of tunnel junctions the measurement of in such a system can provide
direct information about the energy-resolved anomalous Green's function
components describing SRTC and LRTC. (ii) In some cases the exchange
field-suppressed supercurrent can be not only recovered but also enhanced with
respect to its value for non-magnetic junction with the same interface
resistances by the presence of spin-dependent quasiparticle distribution. This
effect is demonstrated for S/N/S junction with magnetic S/N interfaces. In
addition, it is also found that under the considered conditions the dependence
of the Josephson current on temperature can be nontrivial: at first the current
rises upon temperature increasing and only after that starts to decline.Comment: 19 pages, 9 figures, published version, presentation improve
Scattering and pair production by a potential barrier
Scattering and electron-positron pair production by a one-dimensional
potential is considered in the framework of the matrix formalism. The
solutions of the Dirac equation are classified according to frequency sign. The
Bogoliubov transformation relating the in- and out-states are given. We show
that the norm of a solution of the wave equation is determined by the largest
amplitude of its asymptotic form when . For a number of
potentials we give the explicit expressions for the complete in- and out-sets
of orthonormalized wave functions. We note that in principle virtual vacuum
processes in external field influence the phase of wave function of scattered
particle..Comment: 13 pages, LATEX 2e, no figure
Angular distribution of high-energy photoproduction close to the end of spectrum
We consider the differential cross section of electron-positron pair
production by a high-energy photon in a strong Coulomb field close to the end
of the electron or positron spectrum. When the momentum transfer largely
exceeds the electron mass, the cross section is obtained analytically in a
compact form. Coulomb corrections essentially modify the cross section even for
moderate values of the nuclear charge number . In the same kinematical
region, the angular distribution for bound-free pair production,
bremsstrahlung, and photorecombination is also obtained.Comment: 12 pages, 4 figure
Topological Hall Effect in Inhomogeneous Superconductors
We propose a possible mechanism of topological Hall effect in inhomogeneous
superconducting states. In our scenario, the Berry phase effect associated with
spatially modulated superconducting order parameter gives rise to a fictitious
Lorentz force acting on quasiparticles. In the case of the
Fulde-Ferrell-Larkin-Ovchinnikov state, the topological Hall effect is detected
by applying an electromagnetic wave with a tuned wave number on a surface of
the system.Comment: 4 page
On the nature of change in Ni oxidation state in BaTiO3-SrTiO3 system
XAFS studies of Ni-doped BaSrTiO solid solution reveal that
the Ni oxidation state changes from 4 in SrTiO to 2.5 in BaTiO when
varying . This change is accompanied by a noticeable change in the
interatomic Ni-O distances in the first shell. The first-principles
calculations show that nickel creates an impurity band in the forbidden band
gap of BaTiO and SrTiO, which explains the appearance of intense
absorption of Ni-doped samples in the visible region. The analysis of the
electronic structure of doped crystals and calculations of the oxygen vacancy
formation energy in them show that different oxidation states of Ni in
SrTiO and BaTiO can be explained by different formation energies of the
oxygen vacancies in these compounds.Comment: 5 pages, 2 figures, 1 tabl
Multiple M0-brane equations in eleven dimensional pp-wave superspace and BMN matrix model
We obtain the Matrix model equations in the background of the maximally
supersymmetric pp-wave solution of the 11D supergravity and discuss its
relation with the Berenstein-Maldacena-Nastase (BMN) model.Comment: 14 pages, revtex4, no figure
Nodal structure of quasi-2D superconductors probed by magnetic field
We consider a quasi two-dimensional superconductor with line nodes in an
in-plane magnetic field, and compute the dependence of the specific heat, ,
and the in-plane heat conductivity, , on the angle between the field
and the nodal direction in the vortex state. We use a variation of the
microscopic Brandt-Pesch-Tewordt method that accounts for the scattering of
quasiparticles off vortices, and analyze the signature of the nodes in and
. At low to moderate fields the specific heat anisotropy changes sign
with increasing temperature. Comparison with measurements of and
in CeCoIn resolves the contradiction between the two in favor of the
gap.Comment: 5 pages, 3 figure
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