24 research outputs found
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(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(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
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
Tunability of Superconducting Metamaterials
Metamaterials are artificial structures with unique electromagnetic
properties, such as relative dielectric permittivity and magnetic permeability
with values less than 1, or even negative. Because these properties are so
sensitive to loss, we have developed metamaterials comprised of superconducting
waveguides, wires, and split-ring resonators. An important requirement for
applications of these metamaterials is the ability to tune the frequency at
which the unique electromagnetic response occurs. In this paper we present
three methods (unique to superconductors) to accomplish this tuning:
temperature, dc magnetic field, and rf magnetic field. Data are shown for dc
and rf magnetic field tuning of a single Nb split-ring resonator (SRR). It was
found that the dc field tuning was hysteritic in the resonant frequency data,
while the quality factor, , was less hystertic. The rf power tuning showed
no hysteresis, but did show supression of the at high power.
Magneto-optical images reveal inhomogeneous magnetic vortex entry in the dc
field tuning, and laser scanning photoresponse images for a
YBaCuO SRR reveals the current distribution in the rings.Comment: RexTEX, 4 pages of text with 6 figures plus 1/5 page of references,
submitted for the 2006 Applied Superconductivity Conference; Revised edition:
spelling corrections, and we removed mention of measuring the Current Density
and replaced this with a more explicit definition of what we measure (with
reference
Measurement of Local Reactive and Resistive Photoresponse of a Superconducting Microwave Device
We propose and demonstrate a spatial partition method for the high-frequency
photo-response of superconducting devices correlated with inductive and
resistive changes in microwave impedance. Using a laser scanning microscope, we
show that resistive losses are mainly produced by local defects at microstrip
edges and by intergrain weak links in the high-temperature superconducting
material. These defects initiate nonlinear high-frequency response due to
overcritical current densities and entry of vortices.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Microscopic examination of hot spots giving rise to nonlinearity in superconducting resonators
We investigate the microscopic origins of nonlinear rf response in
superconducting electromagnetic resonators. Strong nonlinearity appearing in
the transmission spectra at high input powers manifests itself through the
emergence of jumplike features near the resonant frequency that evolve toward
lower quality factor with higher insertion loss as the rf input power is
increased. We directly relate these characteristics to the dynamics of
localized normal regions (hot spots) caused by microscopic features in the
superconducting material making up the resonator. A clear observation of
hot-spot formation inside a Nb thin film self-resonant structure is presented
by employing the microwave laser scanning microscope, and a direct link between
microscopic and macroscopic manifestations of nonlinearity is established.Comment: 5 pages, 4 figure