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Register a new userMagnetic field dependence of the critical current in YBa_2Cu_3O_{7-delta}/Au/Nb ramp-zigzag Josephson junctions
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Sebastian Scharinger
Publication date
2012
fields
Physics
and research's language is
English
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We study the critical current I_c dependence on applied magnetic field H for multifacet YBa_2Cu_3O_{7-delta}-Au-Nb ramp-type zigzag Josephson junctions. For many experiments one would like to apply a homogeneous field in the junction plane. However, even tiny misalignments can cause drastic deviations from homogeneity. We show this explicitly by measuring and analyzing I_c vs. H for an 8 facet junction, forming an array of 4times(0-pi)-segments. The ramp angle is theta_r=8^circ. The facet width is 10,mum. H is applied under different angles theta relative to the substrate plane and different angles phi relative to the in-plane orientation of the zigzags. We find that a homogeneous flux distribution is only achieved for an angle theta_happrox 1^circ - 2^circ and that even a small misalignment sim 0.1^circ relative to theta_h can cause a substantial inhomogeneity of the flux density inside the junction, drastically altering its I_c vs. H interference pattern. We also show, that there is a dead angle theta^*_d relative to theta_h of similar magnitude, where the average flux density completely vanishes.
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104 -
W. A. C. Passos
, P. N. Lisboa-Filho
, W. A. Ortiz (Grupo den Supercondutividade e Magnetismo
2000
In this paper we determine the magnetic field dependence of the critical current of a tridimensional disordered Josephson junction array (3D-DJJA). A contactless configuration, employing measurements of the AC-susceptibility, is used to evaluate the average critical current of an array of YBa2Cu3O7-x. The critical field necessary to switch off supercurrents through the weak links at the working temperature is also obtained.
We report the first experimental observation of the two-node thickness dependence of the critical current in Josephson junctions with a ferromagnetic interlayer. Vanishings of the critical current correspond to transitions into pi-state and back into conventional 0-state. The experimental data allow to extract the superconducting order parameter oscillation period and the pair decay length in the ferromagnet. We develope a theoretical approach based on Usadel equations, which takes into account the spin-flip scattering. Results of numerical calculations are in good agreement with the experimental data.
We study long Josephson junctions with the critical current density alternating along the junction. New equilibrium states, which we call the field synchronized or FS states, are shown to exist if the applied field is from narrow intervals centered around equidistant series of resonant fields, $H_m$. The values of $H_m$ are much higher than the flux penetration field, $H_s$. The flux per period of the alternating critical current density, $phi_i$, is fixed for each of the FS states. In the $m$-th FS state the value of $phi_i$ is equal to an integer amount of flux quanta, $phi_i =mphi_0$. Two types of single Josephson vortices carrying fluxes $phi_0$ or/and $phi_0/2$ can exist in the FS states. Specific stepwise resonances in the current-voltage characteristics are caused by periodic motion of these vortices between the edges of the junction.
We study dynamic fluctuation effects of $YBa_2Cu_3O_{7-delta}$ thin films in zero field around $T_c$ by doing frequency-dependent microwave conductivity measurements at different powers. The length scales probed in the experiments are varied systematically allowing us to analyze data which are not affected by the finite thickness of the films, and to observe single-parameter scaling. DC current-voltage characteristics have also been measured to independently probe fluctuations in the same samples. The combination of DC and microwave measurements allows us to precisely determine critical parameters. Our results give a dynamical scaling exponent $z=1.55pm0.15$, which is consistent with model E-dynamics.
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