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

Spatial and frequency dependencies of local photoresponse of HTS strip-line resonator in regime of two-tone microwave intermodulation excitation

A new phenomenological approach to spatially-resolved research of nonlinear (NL) microwave properties of operating thin-film superconducting resonators is proposed. The approach is based on frequency and spatial singularity of Laser Scanning Microscopy (LSM) images that can be extracted from a set of 2-D patterns representing x-y distribution of the LSM photoresponse, PR(x, y), at fixed third-order intermodulation (IMD) frequencies 2f1-f2 and 2f2-f1 as a result of two-tone resonator microwave excitation at equidistant frequencies f1 and f2 relative to the fundamental resonance, f0. It was shown by us earlier that the total LSM PR(x, y) originates from two independent (resistive, PRR(x, y), and inductive, PRX(x, y)) contributions which can be extracted directly from the LSM images acquired at f1 and f2 by using a method of spatially-resolved complex impedance partition [1]. Here, we show that practically the same manipulation of LSM images at 2f1-f2 and 2f2-f1 can be used to present NL components of IMD LSM PR(x, y) in terms of its independent spatial variations of (i) inductive IMD_IND(x, y) and (ii) resistive IMD_RES(x, y) contributions reflecting the origin of the local sources of microwave NL. [1] A.P. Zhuravel, S.M. Anlage, and A.V. Ustinov, Appl. Phys. Lett., vol. 88, p. 212503, 2006.Comment: 3 pages, 4 figures, submitted to the Seventh International Kharkov Symposium (MSMW'10) Proceeding

Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices

The technique of low-temperature Laser Scanning Microscopy (LSM) has been applied to the investigation of local microwave properties in operating YBa2Cu3O7/LaAlO3 thin-film resonators patterned into a meandering strip transmission line. By using a modified newly developed procedure of spatially-resolved complex impedance partition, the influence of inhomogeneous current flow on the formation of nonlinear (NL) microwave response in such planar devices is analyzed in terms of the independent impact from resistive and inductive components. The modified procedure developed here is dramatically faster than our previous method. The LSM capability to probe the spatial variations of two-tone, third-order intermodulation currents on micron length scales is used to find the 2D distribution of the local sources of microwave NL. The results show that the dominant sources of microwave NL are strongly localized in the resistive domains.Comment: 4 pages, 6 figures, 2-column format,submitted for the 2006 Applied Superconductivity Conferenc

Spatial correlation of linear and nonlinear electron transport in superconducting microwave resonator: laser scanning microscopy analysis

Spatially-resolved techniques of laser scanning microscopy (LSM) have been used to image simultaneously the spatial variations of (i) rf current flow, J$_RF$(x,y), of (ii) areas of resistive dissipation and (iii) the sources of microwave nonlinearity (NL) in an operating superconducting resonator. The RF power dependent spatial evolution of these linear and NL microwave properties in the meander strip YBCO/LAO superconducting resonator have been LSM probed at different temperatures below Tc. The influence of both topologies of the twin-domain YBCO structure and of J$_RF$(x,y) peaks at the edges of superconducting strip line on its NL properties was analyzed in detail with a micron-scale spatial resolution. Result shows the resistive origin of the dominant sources of microwave NLsComment: 3 pages, 3 figures, submitted to MSMW-07 Symposium Proceeding

Imaging Local Sources of Intermodulation in Superconducting Microwave Devices

This work presents new experimental results on low-temperature (LT) characterization of local rf properties of passive superconducting (SC) microwave devices using a novel Laser Scanning Microscope (LSM). In this technique, a modulated laser beam is focused onto and scanned over the surface of a resonant SC device to probe the spatial distribution of rf current. The highly localized photo-induced change of the kinetic inductance of the SC device produces both a shift of the resonant frequency f_0 and change of the quality factor Q. An image of these changes is recorded as the laser spot is scanned over the device. We present the first measurements of spatially resolved intermodulation response in a High Temperature Superconducting (HTS) co-planar waveguide resonator, opening up a new window into the local origins of nonlinearity in the HTS materials.Comment: 4 Pages, to be published in IEEE Trans. Appl. Supercond., June 200

Unconventional rf photoresponse from a superconducting spiral resonator

Superconducting thin film resonators employing strip geometries show great promise in rf/microwave applications due to their low loss and compact nature. However, their functionality is limited by nonlinear effects at elevated rf/microwave powers. Here, we show that by using a planar spiral geometry carrying parallel currents in adjacent turns, this limitation can be minimized. We investigate the rf current distributions in spiral resonators implemented with Nb thin films via laser scanning microscopy. The rf current density profile along the width of the individual turns of the resonators reveals an unconventional trend: maximum current in the middle of the structure and decaying toward its edges. This unusual behavior is associated with the circular nature of the geometry and the cancellation of magnetic field between the turns, which is favorable for handling high powers since it allows the linear characteristics to persist at high rf current densities.Comment: 8 pages, 7 figure