38 research outputs found
Superconducting weak bonds at grain boundaries in MgB2
The possibility of preparing bicrystalline Josephson junctions and bolometers based on superconducting MgB2 on specially prepared bicrystalline MgO substrates is investigated. Microbridges 0.85â6.00 ÎŒm in width, intersecting the bicrystalline interface, are formed in epitaxial bicrystalline MgB2 films grown on these substrates. It is found that annealing of bicrystalline samples in oxygen leads to a systematic decrease in the critical current, an increase in the temperature width of the superconducting transition region, and to an improvement of the current-voltage (IV) characteristic, which becomes close in shape to the IV characteristic of a Josephson junction. The response of such a junction to radiation at a frequency of 110 GHz with an amplitude attaining 0.5 mV is measured
Supercurrent in a mesoscopic proximity wire
Recent experiments on the proximity induced supercurrent in mesoscopic normal
wires revealed a surprising temperature dependence. They suggest clean-limit
behavior although the wires are strongly disordered. We demonstrate that this
unexpected scaling is actually contained in the conventional description of
diffusive superconductors and find excellent agreement with the experimental
results. In addition we propose a SQUID-like proximity structure for further
experimental investigations of the effects in question.Comment: 6 pages LaTeX, 4 postscript figures; to appear in J. Low Temp. Phys.
(Proceedings of WSS '96
Dissipative current in SIFS Josephson junctions
We investigate superconductor/insulator/ferromagnet/superconductor (SIFS)
tunnel Josephson junctions in the dirty limit, using the quasiclassical theory.
We consider the case of a strong tunnel barrier such that the left S layer and
the right FS bilayer are decoupled. We calculate quantitatively the density of
states (DOS) in the FS bilayer for arbitrary length of the ferromagnetic layer,
using a self-consistent numerical method. We compare these results with a known
analytical DOS approximation, which is valid when the ferromagnetic layer is
long enough. Finally we calculate quantitatively the current-voltage
characteristics of a SIFS junction.Comment: Proceedings of the Vortex VI conference, to be published in Physica
Multiple order parameter configurations in superconductor/ferromagnet multilayers
214512Quantum Matter and Optic
Resonant tunneling in Y(Dy)Ba2Cu3O7âÎŽ/PrBa2Cu3âxGaxO7âÎŽ/Y(Dy)Ba2Cu3O7âÎŽ ramp-type Josephson junctions
Coherent Charge Transport in Metallic Proximity Structures
We develop a detailed microscopic analysis of electron transport in normal
diffusive conductors in the presence of proximity induced superconducting
correlation. We calculated the linear conductance of the system, the profile of
the electric field and the densities of states. In the case of transparent
metallic boundaries the temperature dependent conductance has a non-monotoneous
``reentrant'' structure. We argue that this behavior is due to nonequilibrium
effects occuring in the normal metal in the presence of both superconducting
correlations and the electric field there. Low transparent tunnel barriers
suppress the nonequilibrium effects and destroy the reentrant behavior of the
conductance. If the wire contains a loop, the conductance shows Aharonov-Bohm
oscillations with the period as a function of the magnetic flux
inside the loop. The amplitude of these oscillations also demonstrates
the reentrant behavior vanishing at and decaying as at relatively
large temperatures. The latter behavior is due to low energy correlated
electrons which penetrate deep into the normal metal and ``feel'' the effect of
the magnetic flux . We point out that the density of states and thus the
``strengh'' of the proximity effect can be tuned by the value of the flux
inside the loop. Our results are fully consistent with recent experimental
findings.Comment: 16 pages RevTeX, 23 Postscript figures, submitted to Phys. Rev.
Microscopic nonequilibrium theory of double-barrier Josephson junctions
We study nonequilibrium charge transport in a double-barrier Josephson
junction, including nonstationary phenomena, using the time-dependent
quasiclassical Keldysh Green's function formalism. We supplement the kinetic
equations by appropriate time-dependent boundary conditions and solve the
time-dependent problem in a number of regimes. From the solutions,
current-voltage characteristics are derived. It is understood why the
quasiparticle current can show excess current as well as deficit current and
how the subgap conductance behaves as function of junction parameters. A
time-dependent nonequilibrium contribution to the distribution function is
found to cause a non-zero averaged supercurrent even in the presence of an
applied voltage. Energy relaxation due to inelastic scattering in the
interlayer has a prominent role in determining the transport properties of
double-barrier junctions. Actual inelastic scattering parameters are derived
from experiments. It is shown as an application of the microscopic model, how
the nature of the intrinsic shunt in double-barrier junctions can be explained
in terms of energy relaxation and the opening of Andreev channels.Comment: Accepted for Phys. Rev.
Coherent effects in double-barrier Josephson junctions
The general solution for ballistic electronic transport through
double-barrier Josephson junctions is derived. We show the existence of a
regime of phase-coherent transport in which the supercurrent is proportional to
the single barrier transparency and the way in which this coherence is
destroyed for increasing interlayer thickness. The quasiparticle dc current at
arbitrary voltage is determined.Comment: 4 pages, 2 figures, submitted to Phys. Rev.