Microwave-induced flow of vortices in long Josephson junctions

We report experimental and numerical study of microwave-induced flow of vortices in long Josephson junctions at zero dc magnetic field. Our intriguing observation is that applying an ac-bias of a small frequency $f \ll f_p$ and sufficiently large amplitude changes the current-voltage characteristics ($I$-$V$ curve) of the junction in a way similar to the effect of dc magnetic field, well known as the flux-flow behavior. The characteristic voltage $V$ of this low voltage branch increases with the power $P$ of microwave radiation as $V_{s}\propto P^{\alpha}$ with the index $\alpha \simeq 0.5$. Experiments using a low-temperature laser scanning microscope unambiguously indicate the motion of Josephson vortices driven by microwaves. Numerical simulations agree with the experimental data and show strongly {\it irregular} vortex motion. We explain our results by exploiting an analogy between the microwave-induced vortex flow in long Josephson junctions and incoherent multi-photon absorption in small Josephson junctions in the presence of large thermal fluctuations. In the case of long Josephson junctions the spatially-temporal chaos in the vortex motion mimics the thermal fluctuations. In accordance with this analogy, a control of the intensity of chaos in a long junction by changing its damping constant leads to a pronounced change in the shape of the $I$-$V$ curve. Our results provide a possible explanation to previously measured but not yet understood microwave-driven properties of intrinsic Josephson junctions in high-temperature superconductors.Comment: 8 pages, 13 figure

A one-dimensional tunable magnetic metamaterial

We present experimental data on a one-dimensional superconducting metamaterial that is tunable over a broad frequency band. The basic building block of this magnetic thin-film medium is a single-junction (rf-) superconducting quantum interference device (SQUID). Due to the nonlinear inductance of such an element, its resonance frequency is tunable in situ by applying a dc magnetic field. We demonstrate that this results in tunable effective parameters of our metamaterial consisting of 54 SQUIDs. In order to obtain the effective magnetic permeability from the measured data, we employ a technique that uses only the complex transmission coefficient S21

Superconducting RF Metamaterials Made with Magnetically Active Planar Spirals

Superconducting metamaterials combine the advantages of low-loss, large inductance (with the addition of kinetic inductance), and extreme tunability compared to their normal metal counterparts. Therefore, they allow realization of compact designs operating at low frequencies. We have recently developed radio frequency (RF) metamaterials with a high loaded quality factor and an electrical size as small as $\sim$$\lambda$658, ($\lambda$ is the free space wavelength) by using Nb thin films. The RF metamaterial is composed of truly planar spirals patterned with lithographic techniques. Linear transmission characteristics of these metamaterials show robust Lorentzian resonant peaks in the sub- 100 MHz frequency range below the $T_c$ of Nb. Though Nb is a non-magnetic material, the circulating currents in the spirals generated by RF signals produce a strong magnetic response, which can be tuned sensitively either by temperature or magnetic field thanks to the superconducting nature of the design. We have also observed strong nonlinearity and meta-stable jumps in the transmission data with increasing RF input power until the Nb is driven into the normal state. We discuss the factors modifying the induced magnetic response from single and 1-D arrays of spirals in the light of numerical simulations.Comment: 4 pages, 7 figure

Application of the method of discrete ordinates to the solution of the transport equation in the case of an inhomogeneous planetary atmosphere

A version of the method of discrete ordinate (MDO) which can be used for an optically thick inhomogeneous atmosphere was developed. The MDO may be implemented as an algorithm simpler than those proposed earlier. The algorithm is the same for each azimuth dependent component of intensity. The MDO can determine the scattered radiation field over its entire length along the vertical. It is shown the MDO, when used for homogeneous atmospheres is in agreement with the results obtained by other methods

Fluxon Dynamics of a Long Josephson Junction with Two-gap Superconductors

We investigate the phase dynamics of a long Josephson junction (LJJ) with two-gap superconductors. In this junction, two channels for tunneling between the adjacent superconductor (S) layers as well as one interband channel within each S layer are available for a Cooper pair. Due to the interplay between the conventional and interband Josephson effects, the LJJ can exhibit unusual phase dynamics. Accounting for excitation of a stable 2$\pi$-phase texture arising from the interband Josephson effect, we find that the critical current between the S layers may become both spatially and temporally modulated. The spatial critical current modulation behaves as either a potential well or barrier, depending on the symmetry of superconducting order parameter, and modifies the Josephson vortex trajectories. We find that these changes in phase dynamics result in emission of electromagnetic waves as the Josephson vortex passes through the region of the 2$\pi$-phase texture. We discuss the effects of this radiation emission on the current-voltage characteristics of the junction.Comment: 14 pages, 6 figure

Whispering Vortices

Experiments indicating the excitation of whispering gallery type electromagnetic modes by a vortex moving in an annular Josephson junction are reported. At relativistic velocities the Josephson vortex interacts with the modes of the superconducting stripline resonator giving rise to novel resonances on the current-voltage characteristic of the junction. The experimental data are in good agreement with analysis and numerical calculations based on the two-dimensional sine--Gordon model.Comment: 5 pages, 5 figures, text shortened to fit 4 pages, correction of typo

Nonlinear Seebeck Effect in a Model Granular Superconductor

The change of the Josephson supercurrent density of a weakly-connected granular superconductor in response to externally applied arbitrary thermal gradient dT/dx (nonlinear Seebeck effect) is considered within a model of 3D Josephson junction arrays. For dT/dx>(dT/dx)_c, where (dT/dx)_c is estimated to be of the order of 10^4 K/m for YBCO ceramics with an average grain's size of 10 microns, the weak-links-dominated thermopower S (Seebeck coefficient) is predicted to become strongly dT/dx-dependent.Comment: REVTEX, no figure

Studying the impact of intellectual capital at industrial enterprises on their market capitalization

© Canadian Center of Science and Education. The study sets a task of identifying the impact of intellectual capital structure components on the significance of capitalization of industrial sector enterprises of the Russian Federation. The bottom line of the predicted data by method of indicators is: • Human capital has no significant effect on qualitative characteristics of fuel and energy, metallurgic and food industry enterprises. • Customer capital, less than other factors, has an impact on the capitalization of electric power complex, machine building and construction sectors. It is in these sectors that the negative values of variables are recorded. • Least of all structural capital components impact the indicators of mining, metallurgic and electric power enterprises. Maximum value, and hence the influence, the structural capital exerts on construction sector enterprises. This study is a great asset to make up the programmes for effective resources management of non-material character for managers of the enterprises of industrial economic sector