444 research outputs found
Phase-dependent heat transport through magnetic Josephson tunnel junctions
We present an exhaustive study of the coherent heat transport through
superconductor-ferromagnet(S-F) Josephson junctions including a spin-filter
(I) tunneling barrier. By using the quasiclassical Keldysh Green's
function technique we derive a general expression for the heat current flowing
through a S/F/I/F/S junction and analyze the dependence of the thermal
conductance on the spin-filter efficiency, the phase difference between the
superconductors and the magnetization direction of the ferromagnetic layers. In
the case of non-collinear magnetizations we show explicitly the contributions
to the heat current stemming from the singlet and triplet components of the
superconducting condensate. We also demonstrate that the magnetothermal
resistance ratio of a S/F/I/F/S heat valve can be increased by the
spin-filter effect under suitable conditions.Comment: 8 pages; 6 figure
Quantum interference hybrid spin-current injector
We propose a quantum interference spin-injector nanodevice consisting of a
superconductor-normal metal hybrid loop connected to a
superconductor-ferromagnet bilayer via a tunneling junction. We show that for
certain values of the applied voltage bias across the tunnel barrier and the
magnetic flux through the loop the spin-current can be fully polarized.
Moreover, by tuning the magnetic flux one can switch the sign of the spin
polarization. This operation can be performed at frequencies within the tens of
GHz range. We explore the nanodevice in a wide range of parameters, establish
the optimum conditions for its experimental realization and discuss its
possible applications.Comment: 4.5 pages, 4 color figure
Manifestation of a spin-splitting field in a thermally-biased Josephson junction
We investigate the behavior of a Josephson junction consisting of a
ferromagnetic insulator-superconductor (FI-S) bilayer tunnel-coupled to a
superconducting electrode. We show that the Josephson coupling in the structure
is strenghtened by the presence of the spin-splitting field induced in the FI-S
bilayer. Such strenghtening manifests itself as an increase of the critical
current with the amplitude of the exchange field. Furthermore, the effect
can be strongly enhanced if the junction is taken out of equilibrium by a
temperature bias. We propose a realistic setup to assess experimentally the
magnitude of the induced exchange field, and predict a drastic deviation of the
curve ( is the temperature) with respect to equilibrium.Comment: 4.5 pages, 3 color figure
Singlet-triplet conversion and the long-range proximity effect in superconductor-ferromagnet structures with generic spin dependent fields
The long-range proximity effect in superconductor/ferromagnet (S/F) hybrid
nano-structures is observed if singlet Cooper pairs from the superconductor are
converted into triplet pairs which can diffuse into the fer- romagnet over
large distances. It is commonly believed that this happens only in the presence
of magnetic inhomogeneities. We show that there are other sources of the
long-range triplet component (LRTC) of the con- densate and establish general
conditions for their occurrence. As a prototypical example we consider first a
system where the exchange field and spin-orbit coupling can be treated as time
and space components of an effective SU(2) potential. We derive a SU(2)
covariant diffusive equation for the condensate and demonstrate that an
effective SU(2) electric field is responsible for the long-range proximity
effect. Finally, we extend our analysis to a generic ferromagnet and establish
a universal condition for the LRTC. Our results open a new avenue in the search
for such correlations in S/F structures and make a hitherto unknown connection
between the LRTC and Yang-Mills electrostatics.Comment: 5 pages; 1 Figure; updated file with new reference
Detection of ultrafast oscillations in Superconducting Point-Contacts by means of Supercurrent Measurements
We present a microscopic calculation of the nondissipative current through a
superconducting quantum point contact coupled to a mechanical oscillator. Using
the non-equilibrium Keldysh Green function approach, we determine the
current-phase relation. The latter shows that at certain phases, the current is
sharply suppressed. These dips in the current-phase relation provide
information about the oscillating frequency and coupling strength of the
mechanical oscillator. We also present an effective two-level model from which
we obtain analytical expressions describing the position and width of the dips.
Our findings are of relevance for nanomechanical resonators based on
superconducting materials.Comment: 8 pages, 5 figures. Published in Phys. Rev.
Spin-orbit coupling as a source of long-range triplet proximity effect in superconductor-ferromagnet hybrid structures
We investigate the proximity effect in diffusive superconducting hybrid
structures with a spin-orbit (SO) coupling. Our study is focused on the
singlet-triplet conversion and the generation of long-range superconducting
correlations in ferromagnetic elements. We derive the quasiclassical equations
for the Green's functions including the SO coupling terms in form of a
background SU(2) field. With the help of these equations, we first present a
complete analogy between the spin diffusion process in normal metals and the
generation of the triplet components of the condensate in a diffusive
superconducting structure in the presence of SO coupling. From this analogy it
turns out naturally that the SO coupling is an additional source of the
long-range triplet component (LRTC) besides the magnetic inhomogeneities
studied in the past. We demonstrate an explicit connection between an
inhomogeneous exchange field and SO coupling mechanisms for the generation of
the LRTC and establish the conditions for the appearance of the LRTC in
different geometries. We also consider a S/F bilayer in contact with normal
metal with SO coupling and show that the latter can be used as a source for the
LRTC. Our work gives a global description of the singlet-triplet conversion in
hybrids structures in terms of generic spin-fields and our results are
particularly important for the understanding of the physics underlying
spintronics devices with superconductor elements
Manifestation of extrinsic spin Hall effect in superconducting structures: Non-dissipative magnetoelectric effects
We present a comprehensive quasiclassical approach for studying transport
properties of superconducting diffusive hybrid structures in the presence of
extrinsic spin-orbit coupling. We derive a generalized Usadel equation and
boundary conditions that in the normal state reduce to the drift-diffusion
theory governing the spin-Hall effect in inversion symmetric materials. These
equations predict the non-dissipative spin-galvanic effect, that is the
generation of supercurrents by a spin-splitting field, and its inverse -- the
creation of magnetic moment by a supercurrent. These effects can be seen as
counterparts of the spin-Hall, anomalous Hall and their inverse effects in the
superconducting state. Our theory opens numerous possibilities for using
superconducting structures in magnetoelectronics.Comment: 10 pages, 2 figure
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