This thesis has two major topics: (1) Electrostatic Separation of Superconducting Particles from a Mixture of Non-Superconducting Particles. (2) Improvement in fuel atomization by Electrorheology. (1) Based on the basic science research, the interactions between electric field and superconductors, we have developed a new technology, which can separate superconducting granular particles from their mixture with non-superconducting particles. The electric-field induced formation of superconducting balls is important aspect of the interaction between superconducting particles and electric field. When the applied electric field exceeds a critical value, the induced positive surface energy on the superconducting particles forces them to aggregate into balls or cling to the electrodes. In fabrication of superconducting materials, especially HTSC materials, it is common to come across materials with multiple phases: some grains are in superconducting state while the others are not. Our technology is proven to be very useful in separating superconducting grains from the rest non-superconducting materials. To separate superconducting particles from normal conducting particles, we apply a suitable strong electric field. The superconducting particles cling to the electrodes, while normal conducting particles bounce between the electrodes. The superconducting particles could then be collected from the electrodes. To separate superconducting particles from insulating ones, we apply a moderate electric field to force insulating particles to the electrodes to form short chains while the superconducting particles are collected from the middle of capacitor. The importance of this technology is evidenced by the unsuccessful efforts to utilize the Meissner effect to separate superconducting particles from non-superconducting ones. Because the Meissner effect is proportional to the particle volume, it has been found that the Meissner effect is not useful when the superconducting particles are smaller than 45pm. One always come across multi-phase superconducting materials where most superconducting grains are much smaller than 45μm. On the other hand, since our technology is based on the surface effect, it gets stronger when the particles become smaller. Our technology is thus perfect for small superconducting particles and for fabrication of HTSC materials. The area of superconductivity is expected to be very important for 21st Century energy industry. The key for this development is the HTSC materials. We, therefore, expect that our technology will have strong impact in the area. (2) Improving engine efficiency and reducing pollutant emissions are extremely important. Here we report our fuel injection technology based on new physics principle that proper application of electrorheology can reduce the viscosity of petroleum fuels. A small device is thus introduced just before the fuel injection for the engine, producing a strong electric field to reduce the fuel viscosity, resulting in much smaller fuel droplets in atomization. As combustion starts at the interface between fuel and air and most harmful emissions are coming from incomplete burning, reducing the size of fuel droplets would increase the total surface area to start burning, leading to a cleaner and more efficient engine. This concept has been widely accepted as the discussions about future engine for efficient and clean combustion are focused on ultra-dilute mixtures at extremely high pressure to produce much finer mist of fuel for combustion. The technology is expected to have broad applications, applicable to current internal combustion engines and future engines as well. / Physics

Recent developments in the study of Majorana fermions through braid theory have shown that there exists a set of interchanges that allow for the realization of true quantum computation. Alongside these developments there have been studies of topological superconductivity which show the existence of states that exhibit non-Abelian exchange statistics. Motivated by these developments we study the differences between Abelian and non-Abelian topological phase in the vortex state through the Bogoliubov de-Gennes (BdG) formalism. Due to our interests in low-energy states we first implement computationally efficient algorithms for calculating the mean fields and computing eigenpairs in an arbitrary energy window. We have shown that these algorithms adequately reproduce results obtained from a variety of other techniques and show that these algorithms retain spatial inhomogeneity information. Our results show topological superconductivity and vortex states can coexist; providing a means to realize zero-energy bound states, the number of which corresponds to the topological phase. With the use of our methods we present results contrasting the differences between Abelian and non-Abelian topological phase. Our calculations show that an increase in Zeeman field affects numerous parameters within topological superconductors. It causes the order parameter to become more sensitive to temperature variations in addition to a reduced rate of recovery to the bulk value from a vortex core. The increased field suppresses spin-up local density of states (LDOS) in close proximity to the vortex core for low-energy states. Further, it narrows the spectral gap at the lattice centre. Both energy spectrum and LDOS calculations confirm that trivial topological phase have no zero-energy bound states, Abelian phases have an even number, while non-Abelian phases have an odd number.

Superconductor-Insulator-Superconductor (SIS) mixers are now used regularly in sub- millimetre astronomical receivers. They have already achieved sensitivity approaching the quantum limit at frequencies below the superconducting gap of niobium (~680 GHz). Above that, the mixer performance is compromised by losses, unless materials with higher superconducting gap are employed in conjunction with the niobium tunnel junction. In this thesis, we present the development of 700 GHz niobium SIS mixers, employing a unilateral finline taper on a thin Silicon-On-Insulator (SOI) substrate. These mixers are broadband with full on-chip planar circuit integration, and require only a very simple mixer block. They were designed using rigorous 3-D electromagnetic simulator (HFSS), in conjunction with a quantum mixing software package (SuperMix), and have demonstrated good performance with the best noise temperature measured at 143 K. Our mixer devices were fed by multiple flare angle smooth-walled horns, which are easy to fabricated, yet retain the high performance of corrugated horns. The radiation patterns measured from 600–740 GHz have shown good beam circularity, low sidelobe and cross-polarization levels. In this thesis, we also present SIS mixer designs with balanced and sideband separ- ating capability. These mixers employ back-to-back finline tapers, so that the RF and local oscillator (LO) signals can be injected separately without a beam splitter. We have fabricated and tested the performance of the balanced mixers, and analysed their performance thoroughly. We have also investigated a new method of generating LO signals by beating the tones of two infrared lasers. Using the current 16-pixel 350 GHz SIS receiver, HARP-B, we have observed the ¹²CO J=3→2 emission lines from two nearby galaxies. An important result we found is that the ¹²CO J=3→2 correlates strongly with the 8 μm Polycyclic Aromatic Hydrocarbon emission.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21554号 / 理博第4461号 / 新制||理||1640(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 石田 憲二, 教授 前野 悦輝, 教授 松田 祐司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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The study of topological superconductivity has been at the forefront of condensed matter physics for the past few years. Topological superconductors are predicted to have odd parity pairing and host so called Majorana fermions, which are not only of fundamental importance, but also proposed to be building blocks for fault-tolerant quantum computing. In this dissertation, we use point contact spectroscopy to study the pairing symmetry of candidate topological superconducting materials. We study proximity induced superconductivity in the topological insulator Bi2Se3 by a superconducting niobium tip, and propose a model to explain its features in point contact spectra. We further study the nature of the superconductivity in highly doped superconducting topological insulators, including CuxBi2Se3 and Sn1-xInxTe, using both a normal metal gold tip and a superconducting niobium tip. For CuxBi2Se3, we observe a robust zero-bias conductance peak (ZBCP) in the differential conductance spectra with the gold point contact, while with the niobium point contact we find the height of the peak exhibiting unusual non-monotonic temperature dependence. We argue that both observations cannot be explained by Andreev reflection within the standard Blonder-Tinkham-Klapwijk (BTK) model, but signify unconventional superconductivity in the material. For Sn1-xInxTe samples, we observe ZBCP in the differential conductance spectra with the gold point contact, while with the niobium point contact, the temperature dependence of ZBCP is monotonic as expected from conventional theory, leaving the nature of the superconductivity of Sn1-xInxTe still an open question.

This thesis first outlines the testing undertaken on a partial core superconducting transformer under open circuit, short circuit, full load and endurance test conditions. During the endurance test, a failure occurred after 1 minute and 35 seconds. During the failure, voltage dipping and rapid liquid nitrogen boil off was observed. This prompted a failure investigation which concluded that the lack of cooling in the windings was the most probable cause to the failure. Full core transformer and superconductor theories are then introduced. A copper winding transformer model, based on a Steinmetz equivalent circuit and a reverse design method, is described. A superconductor loss model which outlines the different types of losses experienced under AC conditions is used to determine the resistance of the windings in the Steinmetz equivalent circuit. This resistance changes with the magnitude of current and the strength of the magnetic field that is present in the gaps between each layer of the windings. An alternative leakage flux model is then presented, where the flux is modelled based on the combination of the reluctance of the core and the air surrounding the windings. Based on these theories, an iterative algorithm to calculate the resistance of the superconductor is developed. A new design of a 15kVA single phase full core superconducting transformer, operating in liquid nitrogen, is presented. The issues with building the superconducting transformer are outlined. First, a copper mockup of the superconducting transformer was designed where the mockup would have the same tape and winding dimensions as the superconducting transformer, which means the same core can be used for two different sets of windings. This led to designing a core that could be easily taken apart as well as reassembled. Construction of the core, the copper windings and the superconductor windings ensued. The process of cutting the core laminations, insulating the copper and superconductor tapes, and making the steel fasteners and terminations are described. The copper mockup and superconducting transformers was then tested under open circuit, short circuit, different load and endurance conditions at both liquid nitrogen and room temperatures. These test results were then compared with the those from two models. The comparison showed a significant inaccuracy in the reactances in the models. This introduced a correction factor into the superconductor model which ii made it more accurate. However, further work is required to explain and quantify the correction factors for the copper transformer model under different load conditions.

Thesis advisor: Michael J. Naughton / Quasi-one dimensional (Q1D) molecular organic conductors are among the most exciting materials in condensed matter physics, exhibiting nearly every known ground state. They are highly anisotropic, structurally and electronically, and show large oscillatory phenomena in conductivity for magnetic field rotated in different crystalline planes. Several theoretical works have been published to explain these angular magnetoresistance oscillation (AMRO) effects, but the underlying physics remains illunderstood. Here, we present measurements and calculations of magnetotransport in the molecular organic (super)conductor (DMET)₂I₃ which detect and simulate all known AMRO phenomena for Q1D systems. Employing, for the first time, the true triclinic crystal structure in the calculations, these results address the mystery of the putative vanishing of the primary AMRO phenomenon, the Lebed magic angle effect, for orientations in which it is expected to be strongest. They also show a common origin for Lebed and so-called "Lee-Naughton" oscillations, and confirm the generalized nature of AMRO in Q1D systems. Furthermore, we report the temperature dependence of the upper critical magnetic field in (DMET)₂I₃, for magnetic field applied along the intrachain, interchain, and interplane directions. The upper critical field exhibits orbital saturation at low temperature for field in all directions, implying that superconductivity in (DMET)₂I₃ is conventional spin singlet. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

We report changes in the intergranular material and grain morphology of YBa2Cu3O7-x during cyclic anneals between 780 and 980 ºC in oxygen at atmospheric pressure. Two endothermic reactions were detected: (a) the eutectic reaction of YBa2Cu3O7-x with CuO and BaCuO2 at 900 ºC (enthalpy ΔHa) and (b) the peritectic reaction of YBa2Cu3O7-x with CuO at 950 ºC (ΔHb). During the first anneal, only reaction (b) is detected, and although it should only occur if there is an excess of CuO, its signature is present in all published data. Cyclic annealing causes a monotonic decrease in ΔHb and an increase in ΔHa, larger average grain sizes, and greater volume fraction of the superconducting phase. A steady state is reached after 10 cycles at which point ΔHb = 0. We propose a model that explains the origin of the intergranular CuO and the changes in the intergranular material composition with cyclic annealing.

Les matériaux supraconducteurs présentent des propriétés physiques et géométriques particulières qui exigent des approches de modélisation spatio-temporelle fines, où les méthodes classiques trouvent rapidement leurs limites en termes de convergence, de précision et de temps de calcul. Ce dernier peut être très conséquent, ce qui est incompatible avec les problèmes de dimensionnement et d’optimisation. Dans ce contexte, ce travail a pour objectif de développer des approches de modélisation multiphysique rapides pour le dimensionnement et l’optimisation des systèmes à base de supraconducteurs. Un intérêt particulier est porté pour les méthodes intégrales. Les verrous scientifiques à lever, qui constituent également l’originalité du travail, résident dans l’intégration des lois de comportement E(J) des supraconducteurs dans les schémas numériques de ce type de méthodes. Dans ce travail on développe un modèle numérique afin d’étudier la distribution de la densité de courant et d’estimer les pertes AC dans les supraconducteurs à haute température (HTS). Le modèle développé est basé sur une formulation intégro-différentielle en termes de potentiel vecteur électrique dans les deux domaines fréquentiel et temporel. Une campagne de test est menée afin de valider et de bien cerner les possibilités offertes et les limites de cette approche pour la modélisation des supraconducteurs. / Superconducting materials have particular physical and geometric properties that require spatial-temporal modeling approaches fines, where conventional methods quickly reach their limits in terms of convergence, precision and computational time. The latter can be very consistent, which is incompatible with the design and optimization problems. In this context, this work aims to develop rapid multiphysics modeling approaches for the design and optimization of superconductor-based systems. Particular attention is paid to the integral methods. Scientific obstacles to overcome, which also constitute the originality of the work lies in the integration of behavior laws E (J) of superconducting digital patterns of such methods. A numerical model is developed for a rapid computation of eddy currents in multifilamentary high temperature superconductive (HTS) for the evaluation of AC losses. The developed model is based on an integro-differential formulation in terms of the electric vector potential in the frequency and temporal domains. A test campaign is conducted to validate and clearly identify the possibilities and limitations of this approach for modeling superconductors.