Josephson Junctions In Magnetic Field Research Articles

Emission from Josephson junctions with Gaussian distribution of critical currents

The model which allows to obtain the spectrum of emission of systems of Josephson junctions with the inhomogeneous distributions of critical currents along junctions is developed. With the use of this model we study electrical properties of systems in which junctions have the Gaussian distributions of critical currents. In particular, IV-characteristics and power of emission from inhomogeneous junctions with dimensions smaller than the Josephson depth of penetration of magnetic field have been investigated. We showed that for such junctions the dependence of emitted power on voltage (i.e. the spectrum of emission) had maxima at voltages corresponded to Fiske steps in the whole range of voltages, though in the IV-characteristics particularities (nuclei of zero-field steps) were not seen and they could be revealed only in derivatives of these curves. The comparison of our results with similar results which we obtained earlier for long junctions allows to suppose that the investigated mechanism of the formation of zero-field steps is general and it is valid for both long and short junctions. We investigated the averaged on random realizations height of some maximum of emitted power at different values of the Gaussian standard deviation of critical currents and found the square dependence of this height on the dimensionless parameter which characterizes the standard deviation. This result was in agreement with the theory of zero-field steps. We also considered electrical properties and power of emission from the stack of two long interacting with each other Josephson junctions in magnetic field. Each of the junctions had small (about 10-3 %) Gaussian distribution of critical currents. We found that if magnetic field was absent then there were only normal modes in the system (namely, the in-phase mode and the anti-phase mode). Zero-field steps were formed at voltages corresponded to the split even Fiske step. There were only normal modes in the system also when the relation of magnetic field to the value of the magnetic field at which the critical current becomes zero was more than 0.6. When this relation was smaller, other modes existed as well. We supposed that some normal modes could be destroyed because due to magnetic field standing waves were formed at both odd and even Fiske steps, so some modes could be locked with standing waves.

Shapiro steps in Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions in magnetic field

Shapiro steps in Bi2Sr2CaCu2O8+δ (BSCCO) high-Tc superconductor intrinsic Josephson junctions (IJJs) embedded in the external magnetic field applied parallel to the junction surface have been numerically studied by using the unified theory including both the electric and magnetic field couplings between neighboring Josephson junctions. It has been found that (I) the effect of the electric field coupling between neighboring Josephson junctions is not so crucial in the Shapiro steps of BSCCO IJJs, (II) the overall profiles of the I-V characteristics including Shapiro steps calculated for the same external magnetic induction are fairly similar with each other even if the junction lengths differ from each other, (III) the height of the Shapiro step decreases with increasing the external magnetic field but its magnetic field dependence does not so strongly depend on the number of stacked junctions, (IV) a Shapiro step device, which is hard for the external magnetic disturbance, can be made when the value of the SRshunt product is selected to be small for BSCCO IJJs, and (V) the Shapiro step and the flux flow could be treated separately under the presence of the external magnetic field.

Two-dimensional arrays of Josephson junctions in a magnetic field: A stability analysis of synchronized states

We report the results of a Floquet analysis of two-dimensional arrays of resistively and capacitively shunted Josephson junctions in an external transverse magnetic field. The Floquet analysis indicates stable phase locking of the active junctions over a finite range of values of the bias current and junction capacitance, even in the absence of an external load. This stable phase locking is robust against critical current disorder, up to at least a $\ifmmode\pm\else\textpm\fi{}25%$ rms spread in critical currents.

Microwave absorption by a long Josephson junction in magnetic field

Microwave absorption (MA) by a long Josephson junction in external magnetic field is calculated to explain the surface magnetoimpedance of dense ceramic samples of high T c superconductors. The calculations are made for the low frequencies ω ≪ ω 0 in two limiting cases: 1) the semi-infinite junction, L /δ J ≫ max[(ωτ) −1/2 , (ω 0 τ) −1 ], ( L is the junction length, δ J is the Josephson penetration depth, ω 0 is the Josephson plasma frequency, τ is the dissipation parameter); 2) the junction of finite length, L /δ J min [(ωτ) −1/2 , (ω 0 τ) −1 ]. The model is shown to describe qualitatively the main features of the experimental picture of MA in dense high T c ceramics.

X-band radiation from Josephson junctions in magnetic field

Experimental measurements of current-voltage structure and emitted X-band radiation in applied magnetic field from overlap-geometry Josephson tunnel junctions of normalized length about 2 are compared with numerical simulations obtained with the use of a perturbed sine-Gordon model. The simulations furnish the current and field dependence of the oscillation configuration, from which can be calculated average voltages, frequencies, and power spectra. Simulation and experimental results are in good agreement with regard to the lobe structure of the height of the first zero-field step and/or second Fiske step in magnetic field and the field dependence of the radiation frequency within the various lobes, including details such as hysteresis between lobes. The simulations predict an alternation of the dominant frequency component with increasing field that accounts well for the experimental observations.