Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Nb−Al/Alox/NbNb-Al/Al_{ox}/Nb Josephson Tunnel Junctions: New Theory and Experiment

New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched $Nb-Al/Al_{ox}/Nb$ annular Josephson tunnel junctions as a function of the quench time, $\tau_{Q}$. The probability $f_{1}$ to trap a single defect during the N-S phase transition clearly follows an allometric dependence on $\tau_{Q}$ with a scaling exponent $\sigma = 0.5$, 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 $\sigma = 0.25$, 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

New Experiments for Spontaneous Vortex Formation in Josephson Tunnel Junctions

It has been argued by Zurek and Kibble that the likelihood of producing defects in a continuous phase transition depends in a characteristic way on the quench rate. In this paper we discuss an improved experiment for measuring the Zurek-Kibble scaling exponent $\sigma$ for the production of fluxons in annular symmetric Josephson Tunnel Junctions. We find $\sigma \simeq 0.5$. Further, we report accurate measurements of the junction gap voltage temperature dependence which allow for precise monitoring of the fast temperature variations during the quench.Comment: 12 pages, 5 figures, submitted to Phys. Rev.

Static Properties of Small Josephson Tunnel Junctions in a Transverse Magnetic Field

The magnetic field distribution in the barrier of small planar Josephson tunnel junctions is numerically simulated in the case when an external magnetic field is applied perpendicular to the barrier plane. The simulations allow for heuristic analytical solutions for the Josephson static phase profile from which the dependence of the maximum Josephson current on the applied field amplitude is derived. The most common geometrical configurations are considered and, when possible, the theoretical findings are compared with the experimental data.Comment: Submitted to JAP with 24 pages and 14 figure

Zurek-Kibble domain structures: The Dynamics of Spontaneous Vortex formation in Annular Josephson Tunnel Junctions

Phase transitions executed in a finite time show a domain structure with defects, that has been argued by Zurek and Kibble to depend in a characteristic way on the quench rate. In this letter we present an experiment to measure the Zurek-Kibble scaling exponent sigma. Using symmetric and long Josephson Tunnel Junctions, for which the predicted index is sigma = 0.25, we find sigma = 0.27 +/- 0.05. Further, there is agreement with the ZK prediction for the overall normalisation.Comment: To be published in Phys. Rev. Lett

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

Marker free model-based radio-stereometric analysis for evaluation of hip joint kinematics

Orthopaedics, Trauma Surgery and Rehabilitatio

Phase locked 270-440 GHz local oscillator based on flux flow in long Josephson tunnel junctions

The combination of narrow linewidth and wide band tunability makes the Josephson flux flow oscillator (FFO) a perfect on-chip local oscillator for integrated sub-mm wave receivers for, e.g., spectral radio astronomy. The feasibility of phase locking the FFO to an external reference oscillator is demonstrated experimentally. A FFO linewidth as low as 1 Hz (determined by the resolution bandwidth of the spectrum analyzer) has been measured in the frequency range 270-440 GHz relative to a reference oscillator. This linewidth is far below the fundamental level given by shot and thermal noise of the free-running tunnel junction. The results of residual FFO phase noise measurements are also presented. Finally, we propose a single-chip fully superconductive receiver with two superconductor-insulator-superconductor mixers and an integrated phase-locked loop. (C) 2000 American Institute of Physics. [S0034-6748(00)01701-9]