Alec Nelson – 2016

Nelson_3Scanning of the Intermodulation of Superconductor Resonators

Research Advisor: Dr. Stephen Remillard

At the resonant frequency, superconductor resonators produce intermodulation distortions, smaller signals near the resonant frequency. By inducing external microwave signals, it is possible to analyse the patterns of intermodulation distortions (IMD) in several different types of superconductor resonators. These measurements can be used to complement the main peak values like quality factor and frequency shift in order to understand nonlinearities present in the material of the superconductor. Once spatial distributions of IMD have been identified, they can be used to interpret IMD signals from unknown superconductors and identify various defects in the crystal structure. Using a probe outputting two combined tones into the resonator, it was possible to map the whole of a two-dimensional resonator, using the IMD as the z-direction. In order to best resolve the intermodulation distortions, two superconductors were imaged, a hairpin wide-line resonator and a thin, line resonator. A contour plot of the data was then generated, which displays the IMD of the given resonator.

Funding for this project was provided by The Hope College Natural and Applied Sciences Division and Award number DMR-1505617 from the National Science Foundation.

Anna Wormmeester – 2016

Wormmeester_2Spectroscopic Emission from Argon and Nitrogen Microplasmas

Research Advisor: Dr. Stephen Remillard

Many electronics utilize microgaps, and these electronics can produce plasma, whether intended or not, if it was not intended this plasma can damage the electronics. The breakdown condition and spectral emission of nitrogen and argon plasmas were examined in a microgap under microwave excitation. The differences of the plasma discharge were studied in three different microgap sizes, using nitrogen and argon. The breakdown condition was defined as the input power that ignites microplasma, and the breakdown condition exhibited three distinct pressure domains. These three domains were: under 10 torr, 10 – 300 torr and 300 – 700 torr.   A diffraction grating spectrometer was used to test nitrogen and argon by exploring the emission spectra and by comparing the spectra from microgaps to large gaps, revealing peak oppression and enhancement in the microgaps. This enhancement is shown at a gap of 15μm and is then oppressed at a gap of 1.6mm, at a wavelength of 414nm with a 4 -> 5 vibration transition, and at 426nm with a 1 -> 5 vibration transition in N2. This is also shown in Ar at wavelengths of 591.2nm and 419.8nm.

This work was supported by the Hope College Dean for Natural and Applied Sciences and the Hope College Department of Physics, and is based on earlier support from the Michigan Space Grant Consortium.

Richard Huizen – 2016

Huizen_2Evidence for Distinct Sources of Superconducting Nonlinearity

Research Advisor: Dr. Stephen Remillard

The nonlinear response of cuprate superconducting devices present technological hurdles and scientific opportunities.  Intermodulation Distortion (IMD) generated by the nonlinear response is usually undesirable in superconducting devices, however, some devices leverage IMD to their advantage.  By analyzing the magnetic relaxation of IMD in a YBa2Cu3O7 (YBCO) superconducting thin film, the effect of magnetic fluxon dynamics on nonlinear response reveals information about the origins of nonlinearity.  A carrier wave, resonant with the YBCO superconducting circuit, and two off-resonance probe signals were injected into the resonator.  The combination of these three signals locally excited synchronous second and third order IMD (IMD2 and IMD3).  Upon removal of an applied static magnetic field, IMD3 relaxed with a single decay mode while IMD2 relaxed with slow and fast decay modes that are temperature dependent.  The slow process in the IMD2 decay transitioned from concave down to concave up as the superconductor warmed through an inflection temperature.  This temperature dependent transition of decay modality in IMD2 is due to crossing over either the irreversibility line or the surface barrier activation line.  IMD2 and IMD3 exhibited unique dependencies on temperature and magnetic field, therefore, even and odd order nonlinearities must result from different physical mechanisms.

This work was supported by grant No. DMR-1505617 from the National Science Foundation.

Jacob Pledger – 2015

Pledger
Crystalline Channeling of MeV ion beams

Research Advisor: Dr. Stephen Remillard

Thin film strontium titanate (SrTiO3) on single crystal MgO substrate, and thin film strontium manganese oxide (SrMnO3) also on single crystal MgO substrate, are being considered for use in engineered superlattices.  Crystal matching of the films to the substrates is indicated by channeling of an ion beam through the lattice.  With its ability to resolve depth in a sample, Rutherford backscattering of helium ions is used to determine layer thickness and the depth profile of the elemental composition of a sample.  Ion beam channeling occurs when the beam’s incident angle is parallel to crystal planes, or rather normal to the surface. Channeling can occur in well-ordered and pure crystals, providing an indication of sample quality.  Comparison of the backscattering yields at different incident angles will show a drop in yield as the optimum channeling angle is approached.  Channeling is seen with the bulk SrTiO3 sample as well as with the thin film samples.  Even though an 8% lattice mismatch exists between SrMnO3 and MgO, channeling was still evident, although in this case the yield suppression revealed structure around normal incidence.

This work was funded by a seed grant from the Michigan Space Grant Consortium and by the Hope College Natural and Applied Sciences Division.

Alec Nelson – 2015

AlecNelson

Inductive and Resistive Nonlinearities of a Superconductor Resonator

Research Advisor: Dr. Stephen Remillard

This experiment is designed to compare the feedback from an altered superconductor resonator with a conventional, unaltered superconductor resonator. Superconducting transmission lines are patterned on a lanthanum aluminium substrate chip with a geometry that resonates within the microwave range. Nonlinearities, distortion of the signals in the superconductor, can be engineered into the transmission line using an ion beam or other artificial source of radiation. The sample in this experiment, thin-film yttrium barium copper oxide: YBCO, was sent to a facility in Italy to be engineered with a nonlinearity and then characterised in a low temperature (77 K) cryostat. This means that the power dependence of a intrinsic resonator will differ greatly from this sample. Two key figures of merit of superconducting resonators are their critical power, where the power input to the resonator is most absorbed, and critical frequency of the sample, the frequency at which the critical power occurs. Both were found to vary with temperature, and at high incident power the frequency response of the resonator begins to experience deformation. The change of the power response as frequency is swept through (bending) and the hysteresis in the curve (bifurcation) form the core disparities between traditional superconducting resonators and those with engineered nonlinearities.

Funding for this project was provided by The Hope College Natural and Applied Sciences Division and Award number DMR-1206149 from the National Science Foundation.