6 research outputs found
Enhancement of the Josephson current by magnetic field in superconducting tunnel structures with a paramagnetic spacer
The dc Josephson critical current of a (S/M)IS tunnel structure in a parallel magnetic field is
investigated (here S is a superconductor, S/M is a proximity-coupled S and paramagnetic metal M
bilayer, and I is an insulating barrier). We consider the case when, due to Hund’s rule, in the
metal M the effective molecular interaction aligns the spins of the conduction electrons
antiparallel to the localized spins of magnetic ions. It is predicted that for the tunnel structures
under consideration there are conditions such that the destructive action of the internal and the
applied magnetic fields on Cooper pairs is weakened, and increase of the applied magnetic field
causes field-induced enhancement of the critical tunnel current. The experimental realization of
this interesting effect of the interplay between superconductivity and magnetism is also discussed
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
Josephson Current in S-FIF-S Junctions: Nonmonotonic Dependence on Misorientation Angle
Spectra and spin structures of Andreev interface states in S-FIF-S junctions
are investigated with emphasis on finite transparency and misorientation angle
between in-plane magnetizations of ferromagnetic layers in a three-layer
interface. It is demonstrated that the Josephson current in S-FIF-S quantum
point contacts can exhibit a nonmonotonic dependence on the misorientation
angle. The characteristic behavior takes place, if the pi-state is the
equilibrium state of the junction in the particular case of parallel
magnetizations.Comment: 5 pages, 4 figure
Magnetic exchange interaction induced by a Josephson current
We show that a Josephson current flowing through a
ferromagnet-normal-metal-ferromagnet trilayer connected to two superconducting
electrodes induces an equilibrium exchange interaction between the magnetic
moments of the ferromagnetic layers. The sign and magnitude of the interaction
can be controlled by the phase difference between the order parameters of the
two superconductors. We present a general framework to calculate the Josephson
current induced magnetic exchange interaction in terms of the scattering
matrices of the different layers. The effect should be observable as the
periodic switching of the relative orientation of the magnetic moments of the
ferromagnetic layers in the ac Josephson effect.Comment: 12 pages, 7 figure
Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization
We calculate the dc Josephson current for two types of
superconductor-ferromagnet (S/F) Josephson junctions. The junction of the first
type is a S/F/S junction. On the basis of the Eilenberger equation, the
Josephson current is calculated for an arbitrary impurity concentration. If the expression for the Josephson critical current is reduced
to that which can be obtained from the Usadel equation ( is the exchange
energy, is the momentum relaxation time). In the opposite limit
the superconducting condensate oscillates with period and
penetrates into the F region over distances of the order of the mean free path
. For this kind of junctions we also calculate in the case when the F
layer presents a nonhomogeneous (spiral) magnetic structure with the period
. It is shown that for not too low temperatures, the -state which
occurs in the case of a homogeneous magnetization (Q=0) may disappear even at
small values of . In this nonhomogeneous case, the superconducting
condensate has a nonzero triplet component and can penetrate into the F layer
over a long distance of the order of . The junction
of the second type consists of two S/F bilayers separated by a thin insulating
film. It is shown that the critical Josephson current depends on the
relative orientation of the effective exchange field of the bilayers. In
the case of an antiparallel orientation, increases with increasing .
We establish also that in the F film deposited on a superconductor, the
Meissner current created by the internal magnetic field may be both diamagnetic
or paramagnetic.Comment: 13 pages, 11 figures. To be published in Phys. Rev.
Manifestation of triplet superconductivity in superconductor-ferromagnet structures
We study proximity effects in a multilayered superconductor/ferromagnet (S/F)
structure with arbitrary relative directions of the magnetization . If
the magnetizations of different layers are collinear the superconducting
condensate function induced in the F layers has only a singlet component and a
triplet one with a zero projection of the total magnetic moment of the Cooper
pairs on the direction. In this case the condensate penetrates the F
layers over a short length determined by the exchange energy . If
the magnetizations are not collinear the triplet component has, in
addition to the zero projection, the projections . The latter component
is even in the momentum, odd in the Matsubara frequency and penetrates the F
layers over a long distance that increases with decreasing temperature and does
not depend on (spin-orbit interaction limits this length). If the thickness
of the F layers is much larger than , the Josephson coupling between
neighboring S layers is provided only by the triplet component, so that a new
type of superconductivity arises in the transverse direction of the structure.
The Josephson critical current is positive (negative) for the case of a
positive (negative) chirality of the vector . We demonstrate that this
type of the triplet condensate can be detected also by measuring the density of
states in F/S/F structures.Comment: 14 pages; 9 figures. Final version, to be published in Phys. Rev.