Stephen K. Remillard

Three-tone intermodulation distortion generated by superconducting bandpass filters

Microwave bandpass filters constructed from materials exhibiting some nonlinearity, such as superconductors, will generate intermodulation distortion (IMD) when subjected to signals at more than one frequency. In commercial applications of superconductive receive filters, it is possible for IMD to be generated when a weak receive signal mixes with very strong out-of-band signals, such as those coming from the transmitter. A measurement procedure was developed and data were taken on several different types of superconducting bandpass filters, all developed for commercial application. It was found that in certain interference situations, the three-tone mixing can produce a spur that is noticeable by the receiver, but that there are simple preventative design solutions.

High-temperature superconducting multi-band radio-frequency metamaterial atoms

We report development and measurement of a micro-fabricated compact high-temperature superconducting (HTS) metamaterial atom operating at a frequency as low as ∼53 MHz. The device is a planar spiral resonator patterned out of a YBa2Cu3O7−δ thin film with the characteristic dimension of ∼λ0/1000, where λ0 is the free-space wavelength of the fundamental resonance. While deployment of a HTS material enables higher operating temperatures and greater tunability, it has not compromised the quality of our spiral metamaterial atom and a Q as high as ∼1000 for the fundamental mode, and ∼30 000 for higher order modes, are achieved up to 70 K. Moreover, we have experimentally studied the effect of the substrate by comparing the performance of similar devices on different substrates.

Using a Re-entrant Microwave Resonator to Measure and Model the Dielectric Breakdown Electric Field of Gases

A gas will breakdown in a high electric fleld and the mechanisms of this breakdown at DC and high frequency flelds have been an object of study for the past century. This paper describes a method to induce breakdown in a uniform microwave fleld using a re-entrant sub-quarter wave resonator. Slaters theorem is used to determine the magnitude of the threshold electric fleld at which breakdown occurs. The breakdown threshold is modeled using the efiective electric fleld concept, showing that breakdown varies with pressure as Ebd = CP m ‡ 1 + (!=B ¢ P) 2 ·1=2 where P is the pressure, B and C are flt parameters, and m was found experimentally to equal 1/2. This function exhibits a minimum at Pmin = !=B. Breakdown data from the literature for nitrogen at various microwave frequencies were found to exhibit breakdown minima at the pressure predicted by our own determination of B, further validating the model.

High-Temperature Superconducting Spiral Resonator for Metamaterial Applications

This work studies high-temperature superconducting spiral resonators as a viable candidate for realization of RF/microwave metamaterial atoms. The theory of superconducting spiral resonators is discussed in detail, including the mechanism of resonance, the origin of higher order modes, the analytical framework for their determination, the effects of coupling scheme, and the dependence of the resonance quality factor and insertion loss on the parity of the mode. All the aforementioned models are compared with the experimental data from a microfabricated YBa2Cu3O7-δ (YBCO) spiral resonator. Moreover, the evolution of the resonance characteristics for the fundamental mode with variation of the operating temperature and applied RF power is experimentally examined, and its implications for metamaterial applications are addressed.

Imaging the Anisotropic Nonlinear Meissner Effect in Nodal YBa 2 Cu 3 O 7 − δ Thin-Film Superconductors

We have directly imaged the anisotropic nonlinear Meissner effect in an unconventional superconductor through the nonlinear electrodynamic response of both (bulk) gap nodes and (surface) Andreev bound states. A superconducting thin film is patterned into a compact self-resonant spiral structure, excited near resonance in the radio-frequency range, and scanned with a focused laser beam perturbation. At low temperatures, direction-dependent nonlinearities in the reactive and resistive properties of the resonator create photoresponse that maps out the directions of nodes, or of bound states associated with these nodes, on the Fermi surface of the superconductor. The method is demonstrated on the nodal superconductor YBa2Cu3O7-δ and the results are consistent with theoretical predictions for the bulk and surface contributions.

Effect of LaAlO3 Twin-domain Topology on Local DC and Microwave Properties of Cuprate Films

Different imaging modes of low temperature laser scanning microscopy (LTLSM) have been applied to probe local optical and superconducting properties, as well as the spatial variations in thermoelectric and electronic (both dc and rf) transport, in a YBa2Cu3O6.95/LaAlO3 (YBCO/LAO) superconducting microstrip resonator with micron-range resolution. Additionally, the local sources of microwave nonlinearity (NL) were mapped in two-dimensions simultaneously by using the LTLSM in two-tone rf intermodulation distortion contrast mode as a function of (x,y) position of the laser beam perturbation on the sample. The influence of the direction of individual twin-domain YBCO blocks on its NL properties was analyzed in detail. The result shows the direct spatial correlation between NL microwave and dc electronic transport properties of the YBCO film that are imposed by the underlying twin-domain topology of the LAO substrate. In these circumstances, the scale of local NL current densities JIM(x,y) in different areas of...

A novel ultra-compact resonator for Superconducting thin-film filters

This paper proposes a novel thin-film resonator structure, which combines the microstrip resonator and the coplanar resonator to form an integrated resonator. This resonator structure has an extremely compact size, as compared to the thin-film resonator structures from the literature, and its resonant frequency was shown theoretically to be less sensitive to, or even insensitive to, the thickness of the substrate. An eight-pole quasi-elliptic filter based on this novel resonator was designed. The exact filter layout was simulated and optimized by full-wave electromagnetic simulation using IE3D software. The full-wave simulated filter response was in good agreement with the theoretical filter response. A filter was fabricated on a double-sided YBa/sub 2/Cu/sub 3/O/sub 7/ thin film epitaxially grown on a 2-in-diameter MgO wafer. The measured filter response showed a bandwidth of 1.5 MHz and a center frequency of 850.3 MHz at 78 K. The insertion loss at the passband center was 1 dB, corresponding to a filter Q of 28 000. Steep rejection slopes were obtained at the band edges and rejections reached over 70 dB in approximately 300 kHz from the passband edges. No pronounced changes were observed for input power levels between -20-0 dBm, indicating a relatively high power-handling capability of the filter.

Low temperature thermopower and electrical conductivity in highly conductive CuInO2 thin films

This is the first report on the detailed study on low temperature (6–300 K) electrical conductivity and Seebeck coefficient on copper indium oxide polycrystalline thin films deposited on soda lime glass substrates by a reactive evaporation method. These films, characterized using various experimental techniques, show the highest electrical conductivity (20 to 125 S cm−1) reported to date as well as n- and p- type conductivity. The electrical conductivity mechanisms, based on Motts, Setos and Arrhenius models, in different temperature regimes, comprise of variable range hopping, grain boundary effect and activated thermal conduction. Most interestingly, the thin films manifest a high thermoelectric power factor and absorption in the UV region, indicating their potential in thermoelectric and UV energy conversion device fabrication, respectively.

Synchronous measurement of even and odd order intermodulation distortion at the resonant frequency of a superconducting resonator

A method has been developed that uses three input tones to measure both even and odd order intermodulation distortions (IMDs) inside the pass band of resonant devices. With this technique the surface current density of both the driving signal and the IMD tones can be quantified. Synchronous, or same frequency, measurement of both even and odd order distortions permits quantitative comparison of the respective nonlinearity currents measured within the same time scale. As an example of this technique, a superconducting resonator is used to generate even and odd order IMDs at the same frequency, resulting in physical conclusions, which are pertinent to current research in high temperature superconductors. While varying the level of only one tone, the expected slope of the IMD current versus the driving signal current for both orders is unity, but that is only observed at high temperature when the superconductor becomes very lossy. An observed smaller slope at lower temperatures gives support to the linear-nonlinear interaction model. Also, a sharp increase in the third order IMD relative to the second order IMD near T(C) gives support to a substantial nonlinear Meissner effect.

Electrochemical Synthesis of Novel Zn-Doped TiO2 Nanotube/ZnO Nanoflake Heterostructure with Enhanced DSSC Efficiency

The paper reports the fabrication of Zn-doped TiO2 nanotubes (Zn-TONT)/ZnO nanoflakes heterostructure for the first time, which shows improved performance as a photoanode in dye-sensitized solar cell (DSSC). The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy, scanning electron microscopy, and X-ray diffractometer. The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency, over pure TiO2 photoanodes. Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC.Graphical Abstract