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The initial aim of this thesis was to cool two-dimensional electrons down to temperatures below 10 mK. In order to cool a high mobility two-dimensional electron gas (2DEG) at a GaAs–AlGaAs heterojunction to milliKelvin temperatures, different processing techniques and recipes for low resistance Ohmic contacts based on alloys of Au, Ni, and Ge are fabricated on these semiconductor devices. Scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) images establish that the Ohmic contacts have the same inhomogeneous microstructure observed in the literature. The unexpected result from electrical measurements of the contact resistance RC, the four-terminal resistance along the top of a single contact Rtop, and the vertical resistance RV, is that there is superconductivity in the Ohmic contact below 0.9 K. Measurements for different Ohmic contacts investigated, show some have multiple superconducting transitions, whereas others have a single transition; there is no correlation discovered between the annealing recipe and the number of transitions. I-V measurements show the superconductor is turned completely normal with a DC current of 2.1 mA and in a magnetic field, the superconductor is turned completely normal with a magnetic field of 0.15 T. This thesis speculates on the superconductor, suggesting that the Ohmic contact is a granular superconductor comprised of multiple alloys of different phases, and reviews the possible compounds that may be superconducting below 0.9 K. There is a discussion on how this superconductivity affects electrical transport measurements in similar systems such as quantum conductance, four-terminal Hall measurements and electron cooling experiments in 2DEGs below 0.1 K.

Sulphur has one of the most complex high pressure-temperature phase diagrams of the elements, with many solid phases and multiple liquid phases reported up to 40 GPa (400 kbar). The high temperature stability of solid phases is poorly understood and the melting curve above 12 GPa has been largely unstudied. As pressure and temperature increase, optical and electronic characteristics of sulphur change significantly in both solid and liquid phases. At present there are four generally accepted solid phases up to 83 GPa, above which solid sulphur becomes metallic. Sulphur is thought to be present in multiple planetary cores and is a constituent of H3S, a high pressure-temperature superconductor (TC = 203 K), so understanding its behaviour at extremes is of broad interest. In this thesis, multiple probe techniques have been used to examine phase transformations and transport properties of sulphur at high pressure-temperature conditions, including optical spectroscopy and x-ray diffraction measurements. High pressure conditions have been achieved using the diamond anvil cell, and three heating techniques have been implemented; resistive heating, near-IR (1070 nm) laser heating and mid-IR (10.6 µm) laser heating. Pressures were determined using the ruby fluorescence effect, the diamond edge scale, the equation of state of gold during x-ray studies and by comparing Raman band frequencies to the literature. Stokes to anti-Stokes intensity ratio behaviour was used to measure temperatures alongside thermal emission measurements, and a thermocouple during resistive heating experiments. Sulphur samples were heated to temperatures of ∼1900 K, and compressed to 49.9 GPa. Solid and liquid phase changes were identified using Raman spectra, optical observations, anomalies in laser power vs. temperature dependencies, and x-ray diffraction patterns. The melting curve has been extended up to 45.6 GPa, and an extensive study of the stability regions of solid phases has been made. Multiple liquid phases have been detected, exhibiting different optical absorption properties. The time-domain thermoreflectance technique was also investigated for high pressure samples heated using laser pulses to measure transport (thermal conduction).

Near-field scanning microwave microscopy (NSMM) is a widely used scanning probe microscopy (SPM) technique. It can non-intrusively probe the material properties of a sample at the nano-scale using microwave frequency radiation. The rapid development of nanotechnology, materials and surface science underpinned by scanning probe techniques drives the demand for ever more versatile and non-invasive nano-scale analysis tools. Specifically, the development of solid-state quantum technologies has created a need for nano-scale measurement techniques that operate in the same regime as these quantum devices. However, there are very few nano-scale characterisation tools that are capable of quantum coherent interaction with samples. In particular, all NSMMs so far operate in the 'classical' regime, at high powers. To reach the quantum limit for NSMM we require (i) temperatures that are lower than the photon energy, kbT << hω and (ii) ultra-low power such that the average photon number (n) ~ 1, as is necessary for coherent interaction with a quantum system without saturating it. This work presents an ultra-low power cryogenic NSMM integrated with an atomic force microscope (AFM), to enable precise distance control. A high-quality 6 GHz superconducting resonator is used as the microwave probe. This resonator is micro-machined so that it also forms the scanning tip of the AFM. We show that the microscope is capable of obtaining nano-scale dielectric contrast down to the single microwave photon regime, up to 109 times lower power than in typical NSMMs. The microscope was designed in-house in a dilution refrigerator operating at 10 mK with a customised suspension system to minimise the effects of external mechanical vibrations. In this thesis, we evaluate the performance of this NSMM. We also discuss the remaining challenges towards developing an NSMM capable of quantum coherent interaction, an enabling tool for the development of quantum technologies in the microwave regime.

To achieve ambitious future environmental targets for aircraft set out by organisations such as NASA and the European Union, turboelectric distributed propulsion (TeDP) has been proposed as a novel concept that has the potential to achieve these targets by significantly improving integrated propulsion-airframe performance. Realising TeDP as a technology option brings into play a number of design and development challenges due to the highly integrated natured of TeDP-airframe configurations, low technology-readiness-levels of key enabling technologies and new modes of operation opened up by shift to a more electric architecture. In tackling these challenges a multidisciplinary and integrated method to assess the benefits and challenges of turboelectric and hybrid-electric propulsion system configurations by considering the effect of aircraft size, mission specifications, airframe, electrical system, energy storage, propulsor architecture and gas turbine architecture was created. The method created was used in the assessment of turboelectric and hybrid electric performance for a regional transport aircraft and a medium haul transport aircraft. For the regional role the employment of a DC hybrid superconducting turboelectric architecture managed to achieve 16.7% block fuel saving and 3.23% total energy consumption saving over a baseline turboprop aircraft at 600 n.mi range. Driving performance benefits was increased duration of mission time batteries spend discharging at relatively high battery power rating which overcomes weight penalties from installation of electric machinery. For medium haul role the employment of a geared hybrid electric architecture managed to achieve a 3.07% block fuel saving over a baseline turbofan aircraft at 900 n.mi range. Driving performance benefit for the mission was increased battery-operative-cruise time at relatively high battery power rating overcoming aircraft weight penalty and electric machinery installation weight penalty. Despite fuel burn reduction, hybrid electric aircraft consumes more energy than a baseline configuration primarily due to utilisation of additional energy from battery pack.

We consider the dynamics of Superconducting QUantum Interference Device (SQUID) rings in the presence of time dependent magnetic fields, solving the time dependent Schrodinger equation computationally. We compare the quantum mechanical behaviour of the SQUID ring with that of a simple two state system (the ammonia maser), finding close parallels between these two systems. We then consider the idea of measurement of macroscopic quantum objects by modelling the SQUID ring inductively coupled to a classical measurement device (a LC oscillator circuit). We solve the equations of motion for this coupled system both in the phenomenological Resistively Shunted Junction plus Capacitance (RSJ+C) model and within the framework of two models using a purely quantum mechanical SQUID ring.

Complex metal oxides with structures that are related to high temperature superconducting cuprate phases have been synthesised. The structures and magnetic properties of these materials have been characterised using Rietveld analysis of powder x-ray and powder neutron data and vibrating sample magnetometry. TlSr₂NiO4+δ was synthesised by reaction of Tl₂O₃, Sr₂Ni₂O₅ and SrO in a sealed gold capsule at 950°C. It was found to be isostructural with the orthorhombic form of TlSr₂CuOy, the end member of a series of high temperature superconductors, TlSr₂Can-1O3.5+2n, n = 1, 2, 3, 4. Structural characterisation of the materials using low temperature neutron diffraction indicated a high level of structural similarity between the nickelate and cuprate. Refinement of the occupation of the basal oxygen sites revealed ordering of vacancies along the b cell direction, producing a 2b superlattice and the structure of TlSr₂NiO4+δ contains alternating NiO₆ octahedra and NiO₄ square planes. Both phases were found to display a Curie-Weiss temperature dependence. The related tetragonal cobalt phase, TlSr₂CoO₅, was also synthesised and studied, and differences between it and the orthorhombic nickelate and cuprate were ascribed to the marked oxygen deficiency present in the latter two compounds. An investigation of the Tl-Sr-Ni-La-O system resulted in the isolation of a new family of nickelates described by the formula Tl(Sr₂Ln₂)Ni₂O9, with Ln = La, Pr, Nd, Sm, Eu and Gd. The materials were found to be direct structural analogues of the superconductor Tl(Ba1.6La2.4)Cu₂O9 and crystallise with the 1201-0201 intergrowth structure, consisting of layers of apex-sharing NiO₆ octahedra separated by a TlO layer. The phases are closely related to a series of nickelates, that adopt the K₂NiF₄ structure, and contain stoichiometric NiO₂ layers within the ab-plane. However, the new materials exhibit partial cation ordering with the segregation of the lanthanide and larger strontium ion on two similar crystallographic positions with the structure. A decrease in cell dimensions consistent with the lanthanide contraction was observed for the series. Members of the family containing the smaller lanthanides, Eu and Gd, possess particularly short in-plane nickel-oxygen bonds which are accommodated by the 1201-0201 structure. No evidence of long range magnetic order was found for the lanthanum or gadolinium containing phases. A strontium analogue, Tl(Sr₃La)Cu₂O9, of the original high Tc compound was synthesised as the largest component of a multiphase system and its structure determined from Rietveld analysis of X-ray and neutron diffraction data.

Quantum simulation of material systems is a potentially powerful application of quantum computing. However, the field is currently limited by both the quantity and quality of its hardware. Thus, strategies to mitigate errors are crucial while the number of qubits on a single processing unit continues to grow. Simulating the dynamics of quantum systems is a particularly fruitful area for which these strategies can be applied. In this dissertation, we review some of the recent advances in simulations and prescribe a broad recipe: from encoding a target Hamiltonian to methods of measuring relevant observables and discuss strategies to reduce the effects of noise along the way. The efficacy of utilizing the native cross-resonance gate of IBM’s superconducting hardware as a means to reduce hardware errors is also examined; obtaining promising improvements in the accuracy of the state dynamics of a simple tight binding chain. We additionally study a variational technique to optimize the approximation of time evolution operators for correlated systems. Here wefind modest improvements in the accuracy of the approximated operator for both weakly and strongly correlated Fermi-Hubbard models.

Abstract: This thesis lays out the work required to design and create a platform for cryogenically compatible testing of on-chip microwave resonators, intended as a platform for quantum-limited electromechanical torque sensing. We have created a platform with less than 8 dB loss across an operating range of up to 12 GHz, the widest band we can measure with current equipment. We then used this platform to measure on-chip resonators with quality factors greater than 50, 000, competitive with state-of-the-art devices for which the development and fabrication is also described. We also lay out the necessary theory to design high-quality electromechanical sensors and describe a straightforward path to their creation.

Quantum computers can provide new computational abilities, but only if their intrinsic noise can be suppressed. Quantum error correction (QEC) promises to suppress errors exponentially, provided they are sufficiently uncorrelated. Large arrays of superconducting qubits are a leading platform for implementing quantum error correction, but feature several sources of error that are highly correlated; a single physical process that produces the equivalent of many independent errors to be corrected. These correlated errors must be studied and mitigated in order for quantum error correction to succeed. This thesis addresses two correlated error sources in particular; leakage and impacts from high-energy radiation.Leakage of information out of the states selected for computation presents a significant challenge, as leakage populations spread virally through the device and induce a large pattern of errors if they are not suppressed. We develop several new techniques for removing leakage during QEC codes, eventually achieving regular leakage removal from all qubits, successfully curtailing the ability of leakage to spread. High-energy radiation impacting the device present another problematic error source, as the energies deposited are enough to cause significant error over the entire chip at current sizes. We present time-resolved measurements of such impacts and explain the underlying physical processes with a view toward future mitigation of this error source in hardware.This work understanding and suppressing these correlated errors in our hardware has run parallel to and been integrated into the development of the first scaling demonstrations of surface code quantum error correction.

In harnessing quantum advantages for computation, there is a need for developing high fidelity operations on qubits. An algorithm can be broken down into single qubit operations and multi-qubit entangling gates. However, as the leading quantum processors today are limited to 50-100 qubits and each qubit is sensitive to decoherence noise (often referred to as NISQ era devices), running algorithms with long gate depth is difficult. Understanding the errors that plague existing gates and also expanding the dictionary of available gates is an important part of building a quantum computer. In this thesis we demonstrate two multiqubit gate experiments.In the first experiment we demonstrate a multiqubit entangling gate for superconducting qubits on an all-to-all connected processor that draws upon the advantages of Rabi driven qubits. We also take inspiration from the ion qubit community by using a Mølmer-Sørensen-like interaction through the use of a shared coplanar waveguide (CPW) resonator driven superconducting qubits. We perform sensitivity analysis to understand the parameters that limit our gate fidelities. In the second experiment we introduce and demonstrate a technique for scalable RB of many universal and continuously parameterized gate sets, using a class of circuits called randomized mirror circuits. The technique can be applied to a gate set containing an entangling Clifford gate and the set of arbitrary single-qubit gates, as well as gate sets containing controlled rotations about the Pauli axes. We use our technique to benchmark universal gate sets on four qubits, including a gate set containing a controlled-S gate and its inverse, and we investigate how the observed error rate is impacted by the inclusion of non-Clifford gates. We also show that our technique scales to many qubits with experiments on a 27-qubit IBM Q processor. We use our technique to quantify the impact of crosstalk on this 27-qubit device, and we find that it contributes approximately 2/3 of the total error per gate in random many-qubit circuit layers.

The first part of this dissertation mainly focus on thin film solid oxide fuel cells. In recent years, solid oxide fuel cells are becoming more popular as a green energy source of electricity due to their high efficiency and low carbon emission. However, high operation temperature and materials costs are the main issues impeding the application of this technique. In this presentation, by applying magnetron sputtering technique to fabricate thin film solid oxide fuel cell, we are able to operate the cells under much lower temperature with superior performance under hydrogen or hydrocarbon fuels. Different composite nano-porous cathodes and anodes are fabricated and characterized, all showing reliable, reproducible and scalable results. The second part of the dissertation focus on fabrication and characterizations of spintronic devices, including Si-doped single crystalline Ni nanowires, spin-triplet spintronic and SOT-MRAM devices. Spintronics has been widely applied in data storage applications such as hard disk drives, STT-MRAMs, and SOT-MRAMs, etc. Recently, development of spintronics theories and experiments has allowed it to expand to broader applications, such as domain wall MRAMs, neuromorphic computing and quantum computing. In this section, we will introduce the growth of Si-doped single crystalline Ni nanowires, the effects from AMR, OMR and domain wall MR at low magnetic fields and electron-magnon interaction at high magnetic fields. We studied superconducting triplet spin valve devices. In general, singlet Cooper pairs generated from superconducting layers cannot survive in magnetic layer. However, if we introduce an inhomogeneous moments between these two layers, triplets Cooper pair appeared and can survive much longer than singlet Cooper pair in ferromagnetic materials. In our study, we fabricated epitaxial Ni and Co superconducting spin-triplet spin valves to study this effect. By rotating the soft NiFe layer to break the linearity of magnetizations, inhomogeneous moments can be generated. Magnetization configurations are characterized by polarized neutron reflectometer. By measuring the change of superconducting critical temperature at different angles of external field, we observed that the behavior of spin valve is highly sensitive to the thickness of the inhomogeneous magnetic layers. Lastly, the SOT-MRAM project during the internship in IBM is presented. SOT-MRAM is a potential second generation MRAM compared to STT-MRAM due to its higher efficiency, stability and lower switching current. We fabricated single SOT-MRAM device using $\beta$-W as spin current source. Ion beam etching process, the most critical fabrication process, has been studied. Shapes and aspect ratio effects on nanopillars are discussed. We also introduced thin Hf interlayers in the heterostructure to further decrease the critical switching current. Simulations proves an enhancement in perpendicular anisotropy will lead to this reduction in critical switching current.

Abstract: This thesis describes the design, fabrication, and characterization of 3D superconducting microwave cavities for two applications. It first describes a cryogenically compatible microwave filter that is able to tune its resonant frequency by an unprecedented 5 GHz via deformation caused by a a helium pressure vessel. Then, it describes a novel microwave optomechanics device where such a cavity is coupled to an aluminized SiN membrane. It demonstrates that this device can be back-action cooled from the 450 mK base temperature of the cryostat down to 160 mK.

Particle accelerators are a leading tool for frontier science. Pushing that frontier further demands more machines with higher performance, and more of a very expensive technology: superconducting radio-frequency (SRF) acceleration. From a materials perspective this means reducing residual surface resistance or raising the operating temperature (currently ~2 K) of SRF cavities. Both are pursued by materials modification: nitrogen doping/infusion in the first instance and coating with Nb3Sn in the second. Materials characterization is key to achieving understanding and directing RandD. However, very little has been done. This present work aims to fill the knowledge gap and to provide needed, validated tools to the accelerator science community. In this connection, SIMS, XPS and EBSD have proven especially valuable and represent the majority of discussion in this dissertation.

A Metallic Magnetic Calorimeter (MMC) is a cryogenic calorimetric particle detector that employs a metallic paramagnetic alloy as the temperature sensor material. MMCs are used in many different applications, but this work will focus on their uses in high energy resolution gamma-ray spectroscopy. This technology is of great interest to the field of Nuclear Forensics and Nuclear Safeguards as a non-destructive assay for isotopic analysis of nuclear samples. The energy resolution of MMCs is an order of magnitude higher than the benchmark High Purity Germanium (HPGe) detectors that are currently used in the field and MMCs are also poised to outperform the current leading microcalorimeter, the Transition Edge Sensor (TES). This dissertation will cover the work in development of paramagnetic alloys of Ag and Er as the sensor material, and testing of two generations of devices. The heart of the MMC is the paramagnetic sensor material. The workhorse paramagnet for MMCs is currently an alloy of Au and Er. Although Au:Er is a high performing alloy, it starts to falter at the temperatures below 100 mK which are desirable to maximize the performance of the MMC. Au has a nuclear electric quadrupole moment, which at low temperatures, has its energy levels split by the radial electric fields created by the Er ions. This effect causes the specific heat of the alloy to increase as temperature is lowered, which diminishes device performance. A promising alternate paramagnet is an alloy of Ag and Er. Ag, with both naturally occuring isotopes having a nuclear spin of I=1/2, does not have a nuclear electric quadrupole moment. A technical challenge to working with Ag is that it has such a high affinity for oxygen that the usual method of creating Au:Er alloys may not be sufficient for Ag:Er. Much greater care has to be taken in removing oxygen from the alloy, as during creation the oxygen could adversely alter the Er dopant, thus degrading performance. To combat this, a vacuum induction furnace was developed to achieve the best possible control over synthesis process parameters. Description of the new furnace and test results from a successful synthesis of a Ag:Er alloy are discussed. The other half of the MMC is a high-performing Superconducting Quantum Interfence Device (SQUID) magnetometer. In previously reported devices, it was standard to have the sensing coil, magnetizing circuit, and paramagnet be on a separate chips from the SQUID magnetometer. The approach taken at UNM has been to integrate the SQUID magnetometer and paramagnetic sensor onto a single chip. Having an integrated device increases the performance of the MMC, at the cost of a more difficult fabrication process. Two exploratory wafers of magnetometers have been fabricated and tested for use as MMCs. The first wafer is a set of exploratory two-pixel devices, varying almost every aspect of the device to search for optimal device parameters. The second wafer consists of 14-pixel MMC arrays. A process of electroplating gold absorbers to the devices that now contain sensitive SQUIDs has been developed, using a two-mold system to define the legs and body of the absorbers. An initial Fe-55 spectrum from one of the new arrays is shown as a proof of concept measurement.

For quantum computing to become viable, the inherently fallible nature of qubits must be overcome with quantum error correction (QEC). QEC requires coherent qubits, in a configuration compatible with a given QEC scheme, and quantum logic operations with sufficiently low error. In this thesis, we perform a series of targeted experiments to achieve these goals on a path toward realizing the surface code QEC scheme. We first develop the Xmon variant of the transmon qubit, a highly coherent, planar, and frequency tunable superconducting qubit. With coherence demonstrated, we build an array of five Xmon qubits in a configuration compatible with the surface code, and demonstrate quantum logic operations with sufficiently low error to employ the surface code. These logic gates are characterized with randomized benchmarking, a protocol for determining gate error. We find applications of randomized benchmarking beyond the intended use in gate optimization and decoherence characterization, in addition to exploring the fundamental assumptions of randomized benchmarking. Lastly, we build a nine qubit Xmon transmon array and demonstrate correction of environmental bit-flip errors in a precursor to the surface code.

The large range of length scales present within accelerator magnets suggests the incorporation of a hierarchical structure into computational models. Evaluation of the strain state present within the superconducting filaments is necessary in order to determine the critical current of Nb3Sn based magnets. As part of an ongoing investigation at LBNL, a three-dimensional nonlinear multiscale model is developed to investigate the behavior of Nb3Sn filaments due to macroscopic loading. The major building blocks within a superconducting magnet are used to represent each length scale within the multiscale model: Coil, Rutherford cable, strand, filament, Nb3Sn crystal lattice. Using the developed model, loads at the coil level due to precompression, thermal contraction, and Lorenz forces are translated into lattice strain within the Nb3Sn phase of the composite. Jc can then be calculated through use of measurements performed on bulk samples of Nb3Sn. In addition, the physical effects on each scale due to loading is examined. Each level of the hierarchical model is solved using Finite Element Methods, taking into account effects due to thermal contraction and plasticity. A conjugate gradient algorithm is coupled with a Netwon's method with line search in order to solve resulting systems of equations.

Vortex noise in superconductors is due to the motion of quantized flux (vortices) across the surface of the superconductor. This changing magnetic flux gives rise to a voltage which we detect as a noise signal. Previous measurements show that the vortex noise is related to the interaction of the vortices with intrinsic pinning sites which limit vortex motion. These studies show that the noise signal is composed of voltage bursts related to the vortices moving in fits and starts due to the random location and strength of the intrinsic vortex pinning sites. Our samples are composed of a periodic triangular array of holes that serve as vortex pinning sites. These samples show periodic minima in resistance when the vortex/pinning site densities are commensurate. We find a vortex noise signal that is field, current and temperature dependent, arising from the vortices being depinned. We measure the vortex noise to determine if there is a change from uncorrelated vortex depinning below the first matching field where unoccupied pinning sites exist, to highly correlated vortex depinning at the first matching field when the vortexes are commensurate with the pinning lattice. Our measurements show that there is no field dependence in the vortex noise signal, indicating that the vortex depinning is correlated as the lattice is driven by a DC current. We explain this result in terms of the long range order of our pinning lattice and the strength of the vortex-vortex interaction in our 100 nm pinning lattice. Our findings suggest that the vortex noise is dominated by the vortex-vortex not vortex-pinning site interactions.

Fusion energy has been said to be the solution to all the world’s energy problems. The International Thermonuclear Experimental Reactor (ITER) is the flagship project to demonstrate the feasibility of fusion energy. The Central Solenoid (CS), an important component of the reactor, is needed to induce plasma current, initiate, ramp-up, ramp-down, and sustain plasma in a very controlled manner. In order to achieve this, the CS coil packs must be manufactured under controlled conditions. The CS conductor is an advanced cable-in-conduit Nb3Sn superconductor. The CS cable will be made in long continuous sections but with thousands of meter of cable needed, splices will have to be made in the field during construction of the ITER reactor. With the ends of the CS cable being exposed to the environment for an unspecified amount of time, concern has been expressed about the effect of the cable exposure on the quality of the splice. As a result an experimental program was devised to replicate and expedite the environmental damage the cable may see while in the field. The CS cable samples were exposed to 100% humidity at 60, 80, and 100oC for periods ranging from one week to four weeks. Once the samples were soaked for a period of time they were then sintered as would be done in the field. After sintering the mechanical tests were done to determine the load required to push the sintered strands out of the copper sleeve. Initial results obtained with samples having the sleeve thickness of 1.25mm (0.05in) were inconclusive due to the presence of a fold in the copper sleeve formed during the compaction of the sleeve around the cable. To prevent the fold formation, another set of samples were prepared with thicker copper sleeve of 5mm (0.20in). Results from these samples yielded data that was more conclusive and showed a possible correlation between aging temperature and sintering strength. The experimental data suggests that the thin oxide layer formed during the elevated temperature soak at 100% humidity may even be beneficial to the sinter quality.

Distribution systems across most parts of the globe are highly radial in nature. As loads are gradually increased on a particular distribution system, a higher operating current state leading to increased fault current levels is attained. Hence, the relay co-ordination is disturbed and equipments such as feeders and circuit breakers need to be replaced with higher rating so that they can handle the new currents often leading to expensive retrofit costs. The use of fault current limiter (FCL) is proposed to mitigate the effects of high current levels on a distribution system. A comprehensive and up-to-date literature review of FCL technologies is presented. Detailed efforts of an in-house developed behavioral superconducting FCL model are delineated, including FCL control algorithm and its implementation in PSCAD®/EMTDC environment. Results from simulation studies are investigated and compared to an actual FCL commissioned by Z-energy to highlight the effectiveness of a generic model without having to access proprietary details. Extending those concepts, a solid-state and hybrid type of limiter is also modeled and it results discussed. Finally, an impact assessment is conducted on the distribution protection scheme, due to the FCL being inserted and subsequently operated in the distribution system.

Hybrid devices that combine two-dimensional electron systems in GaAs/AlGaAs heterostructures with Al thin films or Al/AlOx/Al tunnel junctions can provide unique tools for the study of the collective behavior of electrons. We present the study two aspects of low-dimensional physics using hybrid devices. An Al/AlOx/Al single electron transistor is used to monitor the properties of a two-dimensional electron gas in a high magnetic field (1-11 Tesla) at low temperatures (15 mK--280 mK). The single electron transistor measures properties of the deep insulating regime of the integer quantum Hall liquid (between Landau levels) which cannot be probed via other methods. We monitor in real time the motion of charge carriers in the quantum Hall liquid after small changes in magnetic field or back gate voltage. The behavior after an increase in magnetic field is found to be identical to that after a change in back gate voltage. Systematic study of this effect in the nu = 2 plateau shows that two electrons accumulate in the bulk for each flux quanta added to the system. An etched antidot (< 1 mum) under the single electron transistor has the small but clear effect of additional charging around the antidot after an increase in magnetic field. The slow equilibration (> 1 hour) in the nu = 2 plateau provides a new method of measuring the extremely low conductivity of the bulk (10-19 - 10-18 1/O). We also studied the superconducting transition of an Al thin film at zero magnetic field using a bilayer device consisting of a thin Al film and a two-dimensional electron gas. By modulating the resistance of the two-dimensional electron gas we are able to measurably vary the dissipation in the Al due to eddy current coupling of the superconducting vortices to the two-dimensional electron gas. The temperature dependence of this effect indicates the presence of thermally excited vortices below Tc. Drag measurements are also performed on this device. We find that radio-frequency interference creates an anomalous drag signal that is similar to previous unexplained observations and agrees quantitatively with analysis based on the non-linearity of the superconductor at the transition.

Spontaneous Raman scattering and femtosecond time-resolved pump-probe spectroscopy are used to study and characterize material properties in superconductors, bulk semiconductors and semiconducting quantum dots. Superconducting gap oscillations are observed for the first time in MgB 2 (Tc = 39 K) and 2H-NbSe2 ( Tc = 7 K). In MgB2, multiple superconducting gap oscillations are observed at 24 cm-1, 103 cm -1 and ∼44 cm-1. These frequencies are in reasonable agreement with other reported experimental results and published theoretical models. Spontaneous Raman measurements on MgB2 show a single strong resonance at 107 cm-1 near the superconducting gap. Consistent with spontaneous Raman measurement, coherent superconducting gap oscillations in 2H-NbSe2 are observed at 18 cm-1 (E symmetry) and 14 cm-1 ( A symmetry). The analysis suggests that a non-Raman mechanism or impurities are responsible for the observed oscillations in MgB2. Spontaneous Raman spectra of MgB2 show a large frequency shift in the optical E2g phonon from 580 cm-1 at 300 K to 630 cm-1 at 3 K due to anharmonicity. The resonance at the superconducting gap frequency shows a strong asymmetric lineshape near Tc, becoming Lorentzian-like near 3 K due to spectral weight gain at low frequencies. In ZnO, a study of the anharmonic properties of the low-frequency E2 optical phonon, using pump-probe spectroscopy, show an unusually long lifetime ∼2 orders of magnitude larger for most optical modes in semiconductors. At 5 K, the frequency and lifetime are (2.9787 +/- 0.0002) THz and (211 +/- 7) ps. The temperature dependence of the lifetime is determined by up-conversion decay contributions, which vanish at zero temperature. The results show that the lifetime is limited by isotopic disorder and that nanosecond lifetimes may be achievable in isotopically-pure samples. In CdTe1-xSex quantum dots, two longitudinal optical phonons and a mixed mode are identified. The amplitude of the optical modes as a function of the laser wavelength agrees with the impulsive stimulated Raman scattering mechanism. At low power densities, the frequency of the optical phonons deviates from spontaneous Raman scattering behavior, which is attributed to impurity state trapping. Size-selective excitation effects for the acoustic phonons are more noticeable in time-domain studies. The difference between the time-domain and spontaneous Raman studies is not understood. Acoustic phonons are observed in CdSe quantum dots at 37 cm-1, 22 cm-1 and 5 cm-1 at 560 nm. The linewidth of the mode at 37 cm-1 shows a strong dependence on dot size and a linear dependence with temperature.

TwinSol is a unique apparatus designed and built as a joint nuclear physics project of the University of Michigan and the University of Notre Dame. TwinSol is installed at the 10 MegaVolt tandem Van de Graaff accelerator facility located on the campus of the University of Notre Dame's Nuclear Structure Laboratory in Notre Dame, Indiana, USA. This device employs a pair of in-line, large bore, air-core persistent-mode superconducting solenoids (Bmax = 6 tesla) to produce, collect, transport and focus secondary beams of low-energy (E/A < 10 MeV) radioactive ions. Reactions induced by these radioactive nuclear beams (RNBs) are studied using several particle detection systems. Such reactions are pertinent to the understanding of nucleosynthesis and nuclear astrophysics. They are also important in expanding our basic understanding of the properties of nuclei as these RNB which have N >> Z or Z >> N often exhibit behavior that is very different from ordinary, non-radioactive nuclei (N &ap; Z). This thesis details the design, installation and initial in-beam tests of the TwinSol apparatus as well as the results of several experiments performed with the system.

We have studied the microwave response of YBa2Cu3O7-δ, Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O high transition temperature superconducting (HTS) thin films by performing power transmission measurements. These measurements were carried out in the temperature range of 300 to 20 K and at frequencies within the range of 30 to 40 GHz. Through these measurements we have determined the magnetic penetration depth (λ), the complex conductivity (σ* = σ1 - jσ2), and the surface resistance (Rs). An estimate of the intrinsic penetration depth (λ ∼ 121 nm) for the YBa2Cu3O7-δ HTS has been obtained from the film thickness dependence of λ. This value compares favorably with the best values reported so far (∼140 nm) in single crystals and high quality c-axis oriented thin films. Furthermore, it was observed that our technique is sensitive to the intrinsic anisotropy of λ in this superconductor. Values of λ are also reported for Bi-based and Tl-based thin films.We observed that for the three types of superconductors, both σ1 and σ2 increased when cooling the films below their transition temperature. This indicates that the temperature dependence of σ1 is not consistent with that expected from the two-fluid model, and also deviates from the values obtained using the Mattis-Bardeen equations based on the BCS theory.Values of Rs comparable to or lower than that for copper at the same frequency and at 77 K were obtained for the YBa2Cu3O7-δ thin films. However, the Rs for the Bi-based and Tl-based films was larger than that of copper for all the measured temperatures. Our Rs measurements were consistent with those performed at 36 GHz on the same films using using resonant cavity techniques. We have fabricated a resonant cavity to measure R s. The measured R s are in good agreement with other reported R s values obtained using resonant cavity techniques if we assume a quadratic frequency dependence for Rs.Our analysis shows that, of the three types of HTS films studied, the YBa2Cu3O7-δ thin films, deposited by laser ablation and off-axis magnetron sputtering are the most promising for microwave applications.

Scanning Hall probe microscopy (SHM) is an important new magnetic imaging technique that allows direct spatial measurement of magnetic structures with high magnetic sensitivity and spatial resolution. This combination of features has allowed us to study aspect of two distinct superconducting systems that would not be possible using other methods. An array of isolated type I superconducting rings at an applied flux of $\phi\sb0/2$ is expected to behave like a two dimensional random field Ising antiferromagnet, with the quantized magnetic-moments of the rings analogous to Ising spins. SQUID magnetometry confirms the antiferromagnetic interaction between rings, while the SHM directly images specific configurations of spins. We find significant antiferromagnetic nearest-neighbor correlations, but no evidence for any long-range ordering. We attribute this to a significant degree of disorder in the system related to small fluctuations in the areas of the rings. Spatial images from the SHM give new insights into the problem of how magnetic fields penetrate the interior of type II superconductors. We observe vortices driven into superconducting samples with two different geometries by ramping an external magnetic field. In a 50 $\mu$m diameter niobium disk, images show remarkable correlated regions where the field has changed by a value different from the external field increment. We identify these regions as resulting from avalanches of correlated bundles of magnetic flux. The flux contained in these bundles decreases at higher magnetic fields and temperatures, while the diameter of the bundles is independent of field and temperature. Field penetration into a 100-$\mu$m-wide strip of niobium is seen to occur in the form of small ($\sim$10 $\mu$m wide) dendritic fingers which grow smoothly as the field is increased. This suggests a growth mechanism of the flux front possibly mediated by the long-range interactions between mesoscopic flux-containing regions. We have also observed vortex motion due to transport currents in these niobium strips. When the critical current is exceeded, certain regions of the sample exhibit field fluctuations on time scales orders of magnitude longer than the travel times of single vortices. Such fluctuations indicate patterns of possible channels of irregular vortex motion that become more uniform with increasing current.

A spectrometer based on an air-core, superconducting solenoid has been constructed, tested, and demonstrated to be useful as a heavy-ion reaction-product collection and detection device. Two detector systems which measure ion energy loss, residual energy, time-of-flight, and position in the detector plane have been developed for use with the spectrometer. This spectrometer is the first which uses an air-core rather than a steel-yoked magnet. The characteristics of the two different designs are compared. The spectrometer's cylindrical symmetry, focusing properties, and large solid angle make it well-suited for several different types of experiments, including reactions with low cross sections and experiments requiring detection of reaction products emitted at small angles to the beam. The optical properties of the spectrometer were determined using alpha-particle sources and elastically scattered particles from an accelerator beam. Simple first-order and ray-tracing calculations are shown to reproduce well the measured effects. The spectrometer was then used in the study of $\sp{18}$O-induced transfer reactions on neutron-rich targets, which resulted in the measurement of the masses of $\sp{30}$Mg, $\sp{108}$Ru, and $\sp{109}$Rh.

Vortices in superconductors exhibit rich dynamical behaviors that are relevant to the physical properties of the material. In this thesis, we use simulations to study the dynamics of flux-gradient-driven vortices in different types of samples. We make connections between the microscopic behavior of the vortices and macroscopic experimentally observable measurements. First, we systematically quantify the effect of the pinning landscape on the macroscopic properties of vortex avalanches and vortex plastic flow. We relate the velocity field, cumulative patterns of vortex flow channels, and voltage noise measurements with statistical quantities, such as distributions of avalanche sizes. Samples with a high density of strong pinning sites produce very broad avalanche distributions. Easy-flow vortex channels appear in samples with a low pinning density, and typical avalanche sizes emerge in an otherwise broad distribution of sizes. We observe a crossover from interstitial motion in narrow channels to pin-to-pin motion in broad channels as the pin density is increased. Second, we also analyze the microscopic dynamics of vortex motion through channels that form river-like fractal networks in a variety of superconducting samples, and relate it to macroscopic measurable quantities such as the power spectrum. As a function of pinning strength, we calculate the fractal dimension, tortuosity, and the corresponding voltage noise spectrum. Above a certain pinning strength, a remarkable universal drop in both tortuosity and noise power occurs when the vortex motion changes from braiding channels to unbraided channels. Third, we also present a new dynamic phase diagram for driven vortices with varying lattice softness that indicates that, at high driving currents, at least two distinct dynamic phases of flux flow appear depending on the vortex-vortex interaction strength. When the flux lattice is soft, the vortices flow in independently moving channels with smectic structure. For stiff flux lattices, adjacent channels become locked together, producing crystalline-like order in a coupled-channel phase. At the crossover lattice softness between these phases, the system produces a maximum amount of voltage noise. Our results relate spatial order with transport and are in good agreement with experiments. Finally, results for anisotropic systems are presented.