This paper presents an initial approach to investigate the feasibility of fabricating FSF heterostructures, for potential applications in spintronics. These FSF stacks could help characterize long...Show moreThis paper presents an initial approach to investigate the feasibility of fabricating FSF heterostructures, for potential applications in spintronics. These FSF stacks could help characterize long-range triplet Cooper pairs that are created at its interfaces. Simulations inform the final design of a 3D FSF stack, composed of one low and one high aspect ratio rectangular shape. Subsequent efforts were directed on the focused ion beam milling of apertures in 1 µm thick Si3N4 membranes that are used for shadow evaporation of the heterostructures. Several stacks of cobalt and niobium were fabricated with these membranes through shadow evaporation. These heterostructures were contacted via electron beam lithography and measured in a vectormagnet cryostat. Results indicate that no long-range triplets were generated inside the FSF stacks. It can be concluded that either the niobium layers did not become superconducting or the magnetization of the two ferromagnets in the stacks were not perpendicular.Show less
On the hunt for spin triplet superconductivity in ferromagnet-superconductor multilayers, additions were made to an RF insert with an open co-planar waveguide. The low loss setup, with a -1dB per...Show moreOn the hunt for spin triplet superconductivity in ferromagnet-superconductor multilayers, additions were made to an RF insert with an open co-planar waveguide. The low loss setup, with a -1dB per GHz characteristic, was used to obtain FMR spectra with a vector network analyzer. A superconducting coil was designed to generate magnetic fields in situ at cryogenic temperatures. Many cobalt-niobium thin film multilayers were created by means of e-beam evaporation. The FMR spectra were recorded at room temperature and cryogenic temperatures as low as 4.5K. The spectra were analyzed to determine the linewidth of the FMR resonance above and below the critical temperature of different thicknesses of the superconducting layer. The initial results are promising, but not sufficient to conclude decreased gilbert damping in the ferromagnet below the Tc of the superconductor.Show less
To study gravity on the quantum scale, highly isolated systems are necessary. These systems can be created by levitating small particles. This thesis documents a project in which we attempt to...Show moreTo study gravity on the quantum scale, highly isolated systems are necessary. These systems can be created by levitating small particles. This thesis documents a project in which we attempt to design a magnetic levitation trap using two flux concentrator coils in an anti-Meissner orientation to levitate 50 µm microspheres. A sample holder is designed which ensures the proper alignment of the coils and thermalization of all the superconducting components using a copper base and top plate. We did not manage to successfully levitate the microsphere, because the microsphere itself most likely does not reach the right temperature for it to become superconducting. However, we do succeed at consistently sending high currents (600 mA) into a flow cryostat without breaking the superconducting state of the coils. This proves that the trap has the potential to become successful.Show less
Current imaging is crucial to condensed matter physics, materials research and industry. State-of-the-art current imaging setups revolve around SQUID-on-tip (SOT) probes, that scan over a sample to...Show moreCurrent imaging is crucial to condensed matter physics, materials research and industry. State-of-the-art current imaging setups revolve around SQUID-on-tip (SOT) probes, that scan over a sample to locally measure magnetic fields and temperature. The resolution of such systems is presently limited by the lack of a robust method to control the probe-sample distance. In this thesis, we develop probes for hybrid microscopy that combine SOT with STM. We theoretically investigate interesting systems, and find that our approach would considerably improve on past magnetic investigations of vortex matter. We use focused-ion-beam milling to fabricate SOT probes on top of a commercial AFM-cantilever, and show these to be very sensitive to changes in applied magnetic field and temperature. We develop a novel readout scheme to simultaneously measure a magnetic and a tunneling signal. We present a proof-of-concept STMSOT probe that displays magnetic sensitivity inside a cryogenic STM setup, and use it as an STM probe to see the topography of a NbSe$_2$ crystal. Our approach will culminate in the development of a STMSOT setup in the near future.Show less
Mapping the local electronic structure on a nm scale has been vital to the understanding of cuprates. Experiments that probe the local DOS with STS have shown the superconducting gap to be...Show moreMapping the local electronic structure on a nm scale has been vital to the understanding of cuprates. Experiments that probe the local DOS with STS have shown the superconducting gap to be inhomogeneous in these compounds [1]. More recently, ARPES experiments on cuprates have shown the gap to fill rather than close, but it is yet unclear what this process looks like locally [2]. Other STS results have shown that the DOS in overdoped Bi-2201 also contains a pronounced peak attributed to the Van Hove singularity [3]. Such a momentum space origin of the peak remains contested, however, as this peak is reported as similarly inhomogeneous in real space. Presented in this thesis is a phenomenological analysis of STS spectra of Bi2Sr2CuO6+δ (Bi-2201) in the far overdoped regime (OD12K and OD3K). Two different fitting models demonstrate that this supposed VHS is responsible for electron-hole asymmetry of the coherence peaks of the superconducting gap by having the peak energy be close to gap size Δ. It it also shown that the gap filling hypothesis holds up with the addition of a phenomenological peak, although the best model for how the gap closes stays undecided on. Aside from fitting, peak detection analysis supports the same conclusions about the VHS. A more general dimensionality reduction approach is applied to investigate relations between features in the local DOS, utilising Principle Component Analysis PCA) and Uniform Manifold Approximation and Projection (UMAP). However no conspicuous clusters were found in the STS data. This thesis paves the way for more complete models of the still poorly-understood LDOS of cuprates and how it varies in real space. Furthermore, the affirmation of a filling gap adds to the evidence pointing to high-temperature superconductivity being limited by phase coherence. [1] Ø. Fischer, M. Kugler, I. Maggio-aprile, C. Berthod, and C. Renner, Scanning tunneling spectroscopy of high-temperature superconductors, 79 (2007). [2] T. J. Reber, S. Parham, N. C. Plumb, Y. Cao, H. Li, Z. Sun, Q. Wang, H. Iwasawa, M. Arita, J. S. Wen, Z. J. Xu, G. D. Gu, Y. Yoshida, H. Eisaki, G. B. Arnold, and D. S. Dessau, Pairing, pair-breaking, and their roles in setting the Tc of cuprate high temperature superconductors, (2015). [3] A. Piriou, N. Jenkins, C. Berthod, I. Maggio-Aprile, and Fischer, First direct observation of the Van Hove singularity in the tunnelling spectra of cuprates, Nature Communications 2, 221 (2011).Show less
Superconducting nanostructures can be used to detect single photons. Here we propose to use electron-beam-induced deposition (EBID) of a superconducting tungsten-carbon alloy to create nanowires...Show moreSuperconducting nanostructures can be used to detect single photons. Here we propose to use electron-beam-induced deposition (EBID) of a superconducting tungsten-carbon alloy to create nanowires that can be used as a transition edge sensor (TES). Determining if these EBID-written nanowires can be used as an efficient TES requires an experimental characterization of its electrothermal properties. We demonstrate two key experiments to characterize a TES and introduce a numerical model to describe a TES with a nanofabricated constriction as a proof-of-concept. We characterize the low frequency impedance of a PTC thermistor and determine its electrothermal properties. We find a thermal conductance $G = 5.1 \pm 0.2 \text{ \textmu W/K}$ and a heat capacity $C = 0.48 \pm 0.03 \text{ \textmu J/K}$ and discuss how to extend these measurements to superconducting nanowires. A remotely controlled experiment is performed on NbTiN nanowires with a nanofabricated constriction. From the measured IV curves we determine the Joule heating and local temperature of the wire from an adapted Skocpol-Beasley-Tinkham model for a resistive transition. This model is valid for low values of the wire resistance. Together, these experiments and the model provide necessary infrastructure to characterize the electrothermal properties of EBID-written nanowires in the near future.Show less
In an effort to control triplet superconductivity in ferromagnetic disks with RF signals a setup was built to support high frequency experiments in a vector magnet cryostat. This setup included the...Show moreIn an effort to control triplet superconductivity in ferromagnetic disks with RF signals a setup was built to support high frequency experiments in a vector magnet cryostat. This setup included the fabrication of on-substrate coplanar waveguides which can be used to couple RF signals to existing devices by fabricating the devices on top of the waveguide. Another component is the addition of a shielding box which can both block low frequency resonances and can make connecting to the on-substrate waveguides more convenient and reliable. To test the setup, ferromagnetic resonance experiments were done on permalloy thin films using a vector network analyser in addition to the vector magnet.Show less
In this work, we use electron-beam-induced deposition (EBID) to create superconducting structures. This is then applied in the fabrication of superconducting devices, which are characterized in low...Show moreIn this work, we use electron-beam-induced deposition (EBID) to create superconducting structures. This is then applied in the fabrication of superconducting devices, which are characterized in low-temperature experiments.Show less
Prior research has demonstrated by theory and simulation that the creation of holes in two-dimensional superconductors by periodic nanopaterning can increase the critical temperature. To test this...Show morePrior research has demonstrated by theory and simulation that the creation of holes in two-dimensional superconductors by periodic nanopaterning can increase the critical temperature. To test this theory it must be implemented experimentally and the resulting critical temperature must be measured. Preceding the modification of these superconductors, the cryogenic resistance-temperature measurement must be tested and optimized. This thesis discusses the steps, and the problems in them, of the measurement process and provides possible explanations and solutions.Show less
We used modern clean room technologies to produce thin nanopatterned superconductors in an aim to increase their critical temperature. These experiments are based on existing simulations which...Show moreWe used modern clean room technologies to produce thin nanopatterned superconductors in an aim to increase their critical temperature. These experiments are based on existing simulations which indicate that a large change in the electron-phonon coupling parameter lambda is attainable. The simulations were explored in an effort to find an optimal hole geometry and an attempt was made to extend them to a hexagonal lattice of atoms. We obtained ~50nm circular holes spaced 120nm on both MoGe and NbSe2 while also producing contacts to measure these small structures.Show less
Ionic liquid gating experiments have been performed on both La2−xSrxCuO4 and SrTiO3. Superconductivity was induced in initially non superconducting La1.95Sr0.05CuO4 by ionic liquid gating with an...Show moreIonic liquid gating experiments have been performed on both La2−xSrxCuO4 and SrTiO3. Superconductivity was induced in initially non superconducting La1.95Sr0.05CuO4 by ionic liquid gating with an upper critical temperature of 15 K. Further investigation revealed that the gating effect in La2−xSrxCuO4 was purely electrochemical, dominated by a faradaic current. Previous ionic liquid gating experiments on SrTiO3 lead to a theory that could explain the effect electrostatically. Further investigation lead to results in conflict with the electrostatic theory.Show less
