442 research outputs found
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
Self-induced magnetic field effects caused by edge currents in parallel array of Josephson junctions
Novel Regime of Operation for Superconducting Quantum Interference Filters
A new operating regime of the Superconducting Quantum Interference Filter
(SQIF) is investigated. The voltage to magnetic field response function, V(H),
is determined by a Fraunhofer dependence of the critical current and magnetic
flux focusing effect in Josephson junctions (F-mode). For SQIF-arrays made of
high-Tc superconducting bicrystal Josephson junctions the F-mode plays a
predominant role in the voltage-field response V(H). The relatively large
superconducting loops of the SQIF are used for inductive coupling to the
external input circuit. It is shown that the output noise of a SQIF-array
measured with a cooled amplifier in the 1-2 GHz range is determined by the
slope of the V(H) characteristic. Power gain and saturation power were
evaluated using low frequency SQIF parameters. Finally, we consider the
influence of the spread in the parameters of Josephson junctions in the
SQIF-array on the V(H) characteristic of the whole structure.Comment: 7 pages, 4 figure
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFS’s) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hill’s equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFS’s. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hill’s equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFS’s. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
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