672 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
Long range statistical fluctuations of the crossed Josephson current
We investigate the crossed Josephson effect in a geometry consisting of a
double ferromagnetic bridge between two superconductors, with tunnel
interfaces. The crossed Josephson current vanishes on average because the
Andreev reflected hole does not follow the same sequence of impurities as the
incoming electron. We show that i) the root mean square of the crossed
Josephson current distribution is proportional to the square root of the
junction area; and ii) the coherent coupling mediated by fluctuations is ``long
range'' since it decays over the ferromagnet phase coherence length ,
larger than the exchange length. We predict a crossed Josephson current due to
fluctuations if the length of the ferromagnets is smaller than and
larger than the exchange length .Comment: 8 pages, 3 figures, modifications in the presentatio
Long ranged singlet proximity effect in ferromagnetic nanowires
Recently a long ranged superconductor/ferromagnet (S/F) proximity effect has
been reported in Co crystalline nanowires [1, Nature, 6 389 (2010)]. Since the
authors of [1] take care to avoid the existence of magnetic domains, the
triplet character of the long ranged proximity effect is improbable. Here we
demonstrate that in the one-dimensional ballistic regime the standard singlet
S/F proximity effect becomes long ranged. We provide an exact solution for the
decay of the superconducting correlations near critical temperature ()
and for arbitrary impurities concentration. In particular we find a specific
regime, between the diffusive and ballistic ones, where the decay length is
simply the electronic mean-free path. Finally possible experiments which could
permit to elucidate the nature of the observed long ranged proximity effect in
Co nanowires are discussed.Comment: 4 page
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
Resonant peak in the density of states in the normal metal / diffusive ferromagnet / superconductor junctions
The conditions for the formation of zero-energy peak in the density of states
(DOS) in the normal metal / insulator / diffusive ferromagnet / insulator /
s-wave superconductor (N/I/DF/I/S) junctions are studied by solving the Usadel
equations. The DOS of the DF is calculated in various regimes for different
magnitudes of the resistance, Thouless energy and the exchange field of the DF,
as well as for various resistances of the insulating barriers. The conditions
for the DOS peak are formulated for the cases of weak proximity effect (large
resistance of the DF/S interface) and strong proximity effect (small resistance
of the DF/S interface).Comment: 4 pages, 4 figure
Vanishing Meissner effect as a hallmark of in-plane FFLO instability in superconductor - ferromagnet layered systems
We demonstrate that in a wide class of multilayered superconductor -
ferromagnet structures (e.g., S/F, S/F/N and S/F/F') the vanishing Meissner
effect signals the appearance of the in-plane Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) modulated superconducting phase. In contrast to the bulk superconductors
the FFLO instability in these systems can emerge at temperatures close to the
critical one and is effectively controlled by the S layer thickness and the
angle between magnetization vectors in the F/F' bilayers. The predicted FFLO
state reveals through the critical temperature oscillations vs the
perpendicular magnetic field component.Comment: 5 pages, 5 figure
Nonsinusoidal current-phase relations and the transition in diffusive ferromagnetic Josephson junctions
We study the effect of the interfacial transparency on the Josephson current
in a diffusive ferromagnetic contact between two superconductors. In contrast
to the cases of the fully transparent and the low-transparency interfaces, the
current-phase relation is shown to be nonsinusoidal for a finite transparency.
It is demonstrated that even for the nearly fully transparent interfaces the
small corrections due to weak interfacial disorders contribute a small
second-harmonic component in the current-phase relation. For a certain
thicknesses of the ferromagnetic contact and the exchange field this can lead
to a tiny minimum supercurrent at the crossover between 0 and states of
the junction. Our theory has a satisfactory agreement with the recent
experiments in which a finite supercurrent was observed at the transition
temperature. We further explain the possibility for observation of a large
residual supercurrent if the interfaces have an intermediate transparency.Comment: 7 pages, 4 figure
Robust coupling of superconducting order parameter in a mesoscale NbN-Fe-NbN epitaxial structure
We report an unconventional and promising route to self-assemble distributed
superconductor-ferromagnet-superconductor (S-F-S) Josephson Junctions on single
crystal [100] MgO. These structures consist of [110] epitaxial nano-plaquettes
of Fe covered with superconducting NbN films of varying thickness. The S-F-S
structures are characterized by strong magnetoresistance (MR) anisotropy for
the in-plane and out-of-plane magnetic fields. The stronger in-plane MR
suggests decoherence of S-F-S junctions whose critical current follows a
(1-T/Tc) and (1-T/Tc)1/2 dependence for T Tc and T<<Tc respectively, in
accordance with the theory of supercurrent transport in such junctions.Comment: 9 pages, 4 figure
Proximity effect in atomic-scaled hybrid superconductor/ferromagnet structures: crucial role of electron spectra
We study the influence of the configuration of the majority and minority spin
subbands of electron spectra on the properties of atomic-scaled
superconductor-ferromagnet S-F-S and F-S-F hybrid structures. At low
temperatures, the S/F/S junction is either a 0 or junction depending on the
energy shift between S and F materials and the anisotropy of the Fermi
surfaces. We found that the spin switch effect in F/S/F system can be reversed
if the minority spin electron spectra in F metal is of the hole-like type
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