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 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 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
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 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 YBaCuO 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 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 and . The interband impurity scatterings decrease
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 . 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
The current-phase relation in Josephson tunnel junctions
The 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 and
components. Two different physical mechanisms are responsible for the sign of
. The first one is the depairing by current which contributes
positively to the 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 - transition,
the calculated second harmonic fully determines the 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
Properties of rough interfaces in superconductors with d-wave pairing
Theoretical model of a rough interface in a superconductor with d-wave symmetry of the order parameter is proposed. The surface roughness is introduced by means of a surface layer with small electronic mean free path. The proximity effect between such a layer and a bulk d-wave superconductor is studied theoretically in the framework of the quasiclassical Eilenberger theory. It is shown that as a result of strong scattering in the interlayer the d-wave component of the order parameter near the interface is reduced while the s-wave component localized near the interface is generated. Angular and spatial structure of the pair potential and the electronic density of states near the interface is calculated. The interplay of the zero-energy (midgap) and finite-energy bound states leads to peculiarities in the energy dependence of the angle-averaged density of states. We argue that the model is relevant for the description of rough interfaces in high Tc superconductors. In the framework of the present approach we calculate the Josephson critical current for several types of junctions with rough interface
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