631 research outputs found
Planar Josephson Tunnel Junctions in a Transverse Magnetic Field
Traditionally, since the discovery of the Josephson effect in 1962, the
magnetic diffraction pattern of planar Josephson tunnel junctions has been
recorded with the field applied in the plane of the junction. Here we discuss
the static junction properties in a transverse magnetic field where
demagnetization effects imposed by the junction geometry and configuration of
the electrodes are important. Measurements of the critical current versus
magnetic field in planar Nb-based high-quality junctions with different
geometry, size and critical current density show that it is advantageous to use
a transverse magnetic field rather than an in-plane field to suppress the
Josephson tunnel current and Fiske resonances in practical applications.Comment: 5 pages, 2 figures, submitted to Journal of Applied Physic
Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Josephson Tunnel Junctions: New Theory and Experiment
New scaling behavior has been both predicted and observed in the spontaneous
production of fluxons in quenched annular Josephson tunnel
junctions as a function of the quench time, . The probability
to trap a single defect during the N-S phase transition clearly follows an
allometric dependence on with a scaling exponent , as
predicted from the Zurek-Kibble mechanism for {\it realistic} JTJs formed by
strongly coupled superconductors. This definitive experiment replaces one
reported by us earlier, in which an idealised model was used that predicted
, commensurate with the then much poorer data. Our experiment
remains the only condensed matter experiment to date to have measured a scaling
exponent with any reliability.Comment: Four pages, one figur
Spontaneous Fluxon Production in Annular Josephson Tunnel Junctions in the Presence of a Magnetic Field
We report on the spontaneous production of fluxons in the presence of a
symmetry-breaking magnetic field for annular Josephson tunnel junctions during
a thermal quench. The dependence on field intensity of the probability
to trap a single defect during the N-S phase transition drastically
depends on the sample circumferences. We show that the data can be understood
in the framework of the Kibble-Zurek picture of spontaneous defect formation
controlled by causal bounds.Comment: Submitted to Phys. Rev. B with 5 figures on Nov. 15, 200
Long Josephson Tunnel Junctions with Doubly Connected Electrodes
In order to mimic the phase changes in the primordial Big Bang, several
"cosmological" solid-state experiments have been conceived, during the last
decade, to investigate the spontaneous symmetry breaking in superconductors and
superfluids cooled through their transition temperature. In one of such
experiments the number of magnetic flux quanta spontaneously trapped in a
superconducting loop was measured by means of a long Josephson tunnel junction
built on top of the loop itself. We have analyzed this system and found a
number of interesting features not occurring in the conventional case with
simply connected electrodes. In particular, the fluxoid quantization results in
a frustration of the Josephson phase, which, in turn, reduces the junction
critical current. Further, the possible stable states of the system are
obtained by a self-consistent application of the principle of minimum energy.Comment: 34 pages, 9 figures, Phys. Rev. B April 201
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