67 research outputs found
Shot noise in diffusive ferromagnetic metals
We show that shot noise in a diffusive ferromagnetic wire connected by tunnel
contacts to two ferromagnetic electrodes can probe the intrinsic density of
states and the extrinsic impurity scattering spin-polarization contributions in
the polarization of the wire conductivity. The effect is more pronounced when
the electrodes are perfectly polarized in opposite directions. While in this
case the shot noise has a weak dependence on the impurity scattering
polarization, it is strongly affected by the polarization of the density of
states. For a finite spin-flip scattering rate the shot noise increases well
above the normal state value and can reach the full Poissonian value when the
density of states tends to be perfectly polarized. For the parallel
configuration we find that the shot noise depends on the relative sign of the
intrinsic and the extrinsic polarizations.Comment: 4 pages, 3 figure
Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters
We study superconductor-ferromagnet bi-layers, not only for s-wave but also
for d-wave superconductors. We observe oscillations of the critical temperature
when varying the thickness of the ferromagnetic layer for both s-wave and
d-wave superconductors. However, for a rotated d-wave order parameter the
critical temperature differs considerably from that for the unrotated case. In
addition we calculate the density of states for different thicknesses of the
ferromagnetic layer; the results reflect the oscillatory behaviour of the
superconducting correlations.Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens.
Matte
Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions
We have performed temperature dependent tunneling conductance spectroscopy on
Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe
counterelectrode was designed to probe the proximity region of the ab-plane of
BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude
and sign dependent on the energy, decaying with increasing distance from the
junction barrier, in conjunction with the theoretical predictions involving
d-wave superconductors coupled with ferromagnets. The conductance oscillates in
antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a
broken time-reversal pairing symmetry are detected and they do not depend on
the geometrical characteristics of the ferromagnetic film.Comment: 4 pages and 4 figures Submitted to Physical Review Letter
Magnetic interference pattern in planar SNS Josephson junctions
We study the Josephson current through a ballistic normal metal layer of
thickness on which two superconducting electrodes are deposited within a
distance of each other. In the presence of an ({\it in-layer}) magnetic
field we find that the oscillations of the critical current with
the magnetic flux are significantly different from an ordinary magnetic
interference pattern. Depending on the ratio and temperature,
-oscillations can have a period smaller than flux quantum ,
nonzero minima and damping rate much smaller than . Similar anomalous
magnetic interference pattern was recently observed experimentally.Comment: 6 pages, 4 figures, Accepted by Phys. Rev.
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
Enhanced superconducting proximity effect in clean ferromagnetic domain structures
We investigate the superconducting proximity effect in a clean magnetic
structure consisting of two ferromagnetic layered domains with antiparallel
magnetizations in contact with a superconductor. Within the quasiclassical
Green's function approach we find that the penetration of the superconducting
correlations into the magnetic domains can be enhanced as compared to the
corresponding single domain structure. This enhancement depends on an effective
exchange field which is determined by the thicknesses and the exchange fields
of the two domains. The pair amplitude function oscillates spatially inside
each domain with a period inversely proportional to the local exchange field.
While the oscillations have a decreasing amplitude with distance inside the
domain which is attached to the superconductor, they are enhancing in the other
domain and can reach the corresponding normal metal value for a zero effective
exchange field. We also find that the corresponding oscillations in the Fermi
level proximity density of states as a function of the second domain's
thickness has an growing amplitude over a range which depends on the effective
exchange field. Our findings can be explained as the result of cancellation of
the exchange fields induced phases gained by an electron inside the two domains
with antiparallel magnetizations.Comment: 7 pages, 4 figure
On the Selfconsistent Theory of Josephson Effect in Ballistic Superconducting Microconstrictions
The microscopic theory of current carrying states in the ballistic
superconducting microchannel is presented. The effects of the contact length L
on the Josephson current are investigated. For the temperatures T close to the
critical temperature T_c the problem is treated selfconsistently, with taking
into account the distribution of the order parameter inside the
contact. The closed integral equation for in strongly inhomogeneous
microcontact geometry ( is the coherence length at
T=0) replaces the differential Ginzburg-Landau equation. The critical current
is expressed in terms of solution of this integral equation. The
limiting cases of and are considered. With
increasing length L the critical current decreases, although the ballistic
Sharvin resistance of the contact remains the same as at L=0. For ultra short
channels with ( is
the Debye frequency) the corrections to the value of critical current I_c(L=0)
are sensitive to the strong coupling effects.Comment: 15 pages LaTex, 3 jpg figure
Semiclassical theory of spin-polarized shot noise in mesoscopic diffusive conductors
We study fluctuations of spin-polarized currents in a three-terminal
spin-valve system consisting of a diffusive normal metal wire connected by
tunnel junctions to three ferromagnetic terminals. Based on a spin-dependent
Boltzmann-Langevin equation, we develop a semiclassical theory of charge and
spin currents and the correlations of the currents fluctuations. In the three
terminal system, we show that current fluctuations are strongly affected by the
spin-flip scattering in the normal metal and the spin polarizations of the
terminals, which may point in different directions. We analyze the dependence
of the shot noise and the cross-correlations on the spin-flip scattering rate
in the full range of the spin polarizations and for different magnetic
configurations. Our result demonstrate that noise measurements in
multi-terminal devices allow to determine the spin-flip scattering rate by
changing the polarizations of ferromagnetic terminals.Comment: 12 pages, 5 figure
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