407 research outputs found
Josephson effect in SIFS-tunnel junctions with domain walls in weak link region
We study theoretically the properties of SIFS type Josephson junctions
composed of two superconducting (S) electrodes separated by an insulating layer
(I) and a ferromagnetic (F) film consisting of periodic magnetic domains
structure with antiparallel magnetization directions in neighboring domains.
The two-dimensional problem in the weak link area is solved analytically in the
framework of the linearized quasiclassical Usadel equations. Based on this
solution, the spatial distributions of the critical current density,
in the domains and critical current, of SIFS structures are calculated
as a function of domain wall parameters, as well as the thickness, and
the width, of the domains. We demonstrate that
dependencies exhibit damped oscillations with the ratio of the decay length,
and oscillation period, being a function of the
parameters of the domains, and this ratio may take any value from zero to
unity. Thus, we propose a new physical mechanism that may explain the essential
difference between and observed experimentally in various
types of SFS Josephson junctions.Comment: The paper will be published in JETP letters vol 101, issue 11, 201
Superconducting Phase Domains for Memory Applications
In this work we study theoretically the properties of S-F/N-sIS type
Josephson junctions in the frame of the quasiclassical Usadel formalism. The
structure consists of two superconducting electrodes (S), a tunnel barrier (I),
a combined normal metal/ferromagnet (N/F) interlayer and a thin superconducting
film (s). We demonstrate the breakdown of a spatial uniformity of the
superconducting order in the s-film and its decomposition into domains with a
phase shift . The effect is sensitive to the thickness of the s layer
and the widths of the F and N films in the direction along the sIS interface.
We predict the existence of a regime where the structure has two energy minima
and can be switched between them by an electric current injected laterally into
the structure. The state of the system can be non-destructively read by an
electric current flowing across the junction
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
Protected 0-pi states in SIsFS junctions for Josephson memory and logic
We study the peculiarities in current-phase relations (CPR) of the SIsFS
junction in the region of to transition. These CPR consist of two
independent branches corresponding to and states of the contact. We
have found that depending on the transparency of the SIs tunnel barrier the
decrease of the s-layer thickness leads to transformation of the CPR shape
going in the two possible ways: either one of the branches exists only in
discrete intervals of the phase difference or both branches are
sinusoidal but differ in the magnitude of their critical currents. We
demonstrate that the difference can be as large as under maintaining
superconductivity in the s layer. An applicability of these phenomena for
memory and logic application is discussed.Comment: 5 pages, 5 figure
Current-phase relations in SIsFS junctions in the vicinity of 0- transition
We consider the current-phase relation (CPR) in the Josephson junctions with
complex insulator-superconductor-ferromagnetic interlayers in the vicinity of
0- transition. We find a strong impact of the second harmonic on CPR of
the junctions. It is shown that the critical current can be kept constant in
the region of 0-pi transition, while the CPR transforms through multi-valued
hysteretic states depending on the relative values of tunnel transparency and
magnetic thickness. Moreover, CPR in the transition region has multiple
branches with distinct ground states.Comment: Submitted in Phys. Rev.
Theory of tunneling spectroscopy of normal metal/ferromagnet/spin-triplet superconductor junctions
We study the tunneling conductance of a ballistic normal metal / ferromagnet
/ spin-triplet superconductor junction using the extended
Blonder-Tinkham-Klapwijk formalism as a model for a -axis oriented Au /
SrRuO / SrRuO junction. We compare chiral -wave (CPW) and
helical -wave (HPW) pair potentials, combined with ferromagnet magnetization
directions parallel and perpendicular to the interface. For fixed ,
where is a direction of magnetization in the ferromagnet measured
from the -axis, the tunneling conductance of CPW and HPW clearly show
different voltage dependencies. It is found that the cases where the -vector
is perpendicular to the magnetization direction (CPW with
and HPW with ) are identical. The obtained results serve as a
guide to determine the pairing symmetry of the spin-triplet superconductor
SrRuO.Comment: 12 pages, 7 figures. There is also a supplementary (not uploaded
Josephson pi-state in a ferromagnetic insulator
We predict anomalous atomic-scale 0-pi transitions in a Josephson junction
with a ferromagnetic-insulator (FI) barrier. The ground state of such junction
alternates between 0- and pi-states when thickness of FI is increasing by a
single atomic layer. We find that the mechanism of the 0-pi transition can be
attributed to thickness-dependent phase-shifts between the wave numbers of
electrons and holes in FI. Based on these results, we show that stable pi-state
can be realized in junctions based on high-Tc superconductors with
LaBaCuO barrier.Comment: 4 pages, 3 figures, Phys. Rev. Lett. (2010) in pres
Andreev reflection in layered structures: implications for high T_c grain boundary Josephson junctions
Andreev reflection is investigated in layered anisotropic normal metal /
superconductor (N/S) systems in the case of an energy gap \Delta in S not
negligible with respect to the Fermi energy E_F, as it probably occurs with
high critical temperature superconductors (HTS). We find that in these limits
retro-reflectivity, which is a fundamental feature of Andreev reflection, is
broken modifying sensitively transport across S/N interfaces. We discuss the
consequences for supercurrents in HTS Josephson junctions and for the midgap
states in S-N contactsComment: 4 pages, 4 figures, to be published in Phys. Rev.
Odd-frequency Pairs and Josephson Current through a Strong Ferromagnet
We study Josephson current in superconductor / diffusive ferromagnet
/superconductor junctions by using the recursive Green function method. When
the exchange potential in a ferromagnet is sufficiently large as compared to
the pair potential in a superconductor, an ensemble average of Josephson
current is much smaller than its mesoscopic fluctuations. The Josephson current
vanishes when the exchange potential is extremely large so that a ferromagnet
is half-metallic. Spin-flip scattering at junction interfaces drastically
changes the characteristic behavior of Josephson current. In addition to
spin-singlet Cooper pairs, equal-spin triplet pairs penetrate into a half
metal. Such equal-spin pairs have an unusual symmetry property called
odd-frequency symmetry and carry the Josephson current through a half metal.
The penetration of odd-frequency pairs into a half metal enhances the low
energy quasiparticle density of states, which could be detected experimentally
by scanning tunneling spectroscopy. We will also show that odd-frequency pairs
in a half metal cause a nonmonotonic temperature dependence of the critical
Josephson current.Comment: 12 pages 14 figures embedde
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