1,097 research outputs found

### Properties of tunnel Josephson junctions with a ferromagnetic interlayer

We investigate superconductor/insulator/ferromagnet/superconductor (SIFS)
tunnel Josephson junctions in the dirty limit, using the quasiclassical theory.
We formulate a quantitative model describing the oscillations of critical
current as a function of thickness of the ferromagnetic layer and use this
model to fit recent experimental data. We also calculate quantitatively the
density of states (DOS) in this type of junctions and compare DOS oscillations
with those of the critical current.Comment: 9 pages, 8 figures, to be published in Phys. Rev.

### Density of states in SF bilayers with arbitrary strength of magnetic scattering

We developed the self-consistent method for the calculation of the density of
states $N(\epsilon)$ in the SF bilayers. It based on the quasi-classical Usadel
equations and takes into account the suppression of superconductivity in the S
layer due to the proximity effect with the F metal, as well as existing
mechanisms of the spin dependent electron scattering. We demonstrate that the
increase of the spin orbit or spin flip electron scattering rates results in
completely different transformations of $N(\epsilon)$ at the free F layer
interface. The developed formalism has been applied for the interpretation of
the available experimental data.Comment: 5 pages, 8 figure

### The current-phase relation in Josephson tunnel junctions

The $J(\phi)$ relation in SFIFS, SNINS and SIS tunnel junctions is studied.
The method for analytical solution of linearized Usadel equations has been
developed and applied to these structures. It is shown that the Josephson
current across the structure has the sum of $\sin \phi$ and $\sin 2\phi$
components. Two different physical mechanisms are responsible for the sign of
$\sin 2\phi$. The first one is the depairing by current which contributes
positively to the $\sin 2\phi$ term, while the second one is the finite
transparency of SF or SN interfaces which provides the negative contribution.
In SFIFS junctions, where the first harmonic vanishes at 0 - $\pi$ transition,
the calculated second harmonic fully determines the $J(\phi)$ curve.Comment: 6 pages, 2 figure

### Manifestation of the odd-frequency spin-triplet pairing state in diffusive ferromagnet / superconductor junctions

Using the quasiclassical Green's function formalism, we study the influence
of the odd-frequency spin-triplet superconductivity on the local density of
states (LDOS) in a diffusive ferromagnet (DF) attached to a superconductor.
Various possible symmetry classes in a superconductor are considered which are
consistent with the Pauli's principle: even-frequency spin-singlet even-parity
(ESE) state, even-frequency spin-triplet odd-parity (ETO) state, odd-frequency
spin-triplet even-parity (OTE) state and odd-frequency spin-singlet odd-parity
(OSO) state. For each of these states, the pairing state in DF is studied.
Particular attention is paid to the study of spin-singlet s-wave and
spin-triplet p-wave superconductors as the examples of ESE and ETO
superconductors. For spin-singlet case the magnitude of the OTE component of
the pair amplitude is enhanced with the increase of the exchange field in DF.
When the OTE component is dominant at low energy, the resulting LDOS in DF has
a zero energy peak (ZEP). On the other hand, in DF / spin-triplet p-wave
superconductor junctions LDOS has a ZEP in the absence of the exchange field,
where only the OTE paring state exists. With the increase of the exchange
field, the ESE component of the pair amplitude induced in DF is enhanced. Then,
the resulting LDOS has a ZEP splitting. We demonstrate that the appearance of
the dominant OTE component of the pair amplitude is the physical reason of the
emergence of the ZEP of LDOS.Comment: 9 pages, 9 figure

### Impurity scattering in highly anisotropic superconductors and interband sign reversal of the order parameter

We discuss various mechanisms that can lead to interband sign reversal of the
order parameter in a multiband superconductor. In particular, we generalize
Abrikosov-Gor'kov solution of the problem of weakly coupled superconductor with
magnetic and nonmagnetic impurities on the case of arbitary order parameter
anisotropy, including extreme cases as $d-$pairing or interband sign reversal
of the order parameter, and show that interband scattering by magnetic
impurities can stabilize an interband sign-reversal state. We discuss a
possibility of such state in YBa$_2$Cu$_3$O$_7$ in the context of various
experiments: Josephson tunneling, neutron scattering, isotope effect
measurements.Comment: 8 pages, 1 psfig. To be published in materials of 1996 SPIE
conference "Spectroscopic Studies of Superconductors". This is a summary of
papers cond-mat/9501117, cond-mat/9501118, cond-mat/9502025,
cond-mat/9504076. Besides, we derive a formula for Tc suppression by magnetic
and nonmagnetic impurities for arbitrary anisotrop

### Green function theory of dirty two-band superconductivity

We study the effects of random nonmagnetic impurities on the superconducting
transition temperature $T_c$ in a two-band superconductor, where we assume the
equal-time spin-singlet s-wave pair potential in each conduction band and the
hybridization between the two bands as well as the band asymmetry. In the clean
limit, the phase of hybridization determines the stability of two states:
called $s_{++}$ and $s_{+-}$. The interband impurity scatterings decrease $T_c$
of the two states exactly in the same manner when the Hamiltonian preserves
time-reversal symmetry. We find that a superconductor with larger hybridization
shows more moderate suppression of $T_c$. This effect can be explained by the
presence of odd-frequency Cooper pairs which are generated by the band
hybridization in the clean limit and are broken by impurities.Comment: 11 pages, 2 figure

### Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor

To guide experimental work on the search for Majorana zero-energy modes, we
calculate the superconducting pairing symmetry of a three-dimensional
topological insulator in combination with an s-wave superconductor. In analogy
to the case of nanowires with strong spin-orbit coupling we show how the
pairing symmetry changes across different topological regimes. We demonstrate
that a dominant p-wave pairing relation is not sufficient to realize a Majorana
zero-energy mode useful for quantum computation. Our main result of this paper
is the relation between odd-frequency pairing and Majorana zero energy modes by
using Green functions techniques in three-dimensional topological insulators in
the so-called Majorana regime. We discuss thereafter how the pairing relations
in the different regimes can be observed in the shape of the tunneling
conductance of an s-wave proximized three-dimensional topological insulator. We
will discuss the necessity to incorporate a ferromagnetic insulator to localize
the zero-energy bound state to the interface as a Majorana mode.Comment: Accepted for publication in Journal of Physics: Condensed Matte

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