Doctor of Philosophy, The Ohio State University, 2020, Mathematical Sciences

This thesis describes four different projects exploring novel aspects of superconductivity in conjunction with topology and strong correlations. First, we address a fundamental question at the heart of the quest for high-temperature superconductivity: how high can the superconducting critical temperature Tc be? We derive rigorous upper bounds on Tc for two-dimensional superconductors via bounds on its stiffness to phase fluctuations. These are most useful for superconductors with strong correlations, where the usual mean-field approximations tend to fail. We calculate the maximum Tc of the recently discovered superconductor in magic-angle twisted bilayer graphene and in monolayer FeSe on SrTiO3 and find that our bound is quite close to the maximum Tc observed in both these fascinating complex systems. For a single band of electrons with parabolic dispersion in two dimensions, we show that Tc is atmost one-eight of the Fermi temperature, which places severe constraints on superconductivity in the simplest condensed matter setting, testable in experiments on ultra-cold Fermi gases. Second, we illuminate the interplay of topology and strong correlations in the normal state of an iron-based superconductor Fe(Se,Te). We show how dipole selection rules of the photoemission matrix elements can provide sharp signatures of the topological band inversion, and present data from our experimental collaborators that tests our theoretical predictions. Third, we explore the interplay of topology and superconductivity in a model which can describe a topological insulator. We find that several exotic new superconducting phases, including two new topological superconductors which reveal a generic new route to topological superconductivity in Dirac materials. Lastly, we employ a variety of analytical and numerical tools to study the emergence of superconductivity from an insulator in a simple model. Our results give insights into the question of how a superconducting instability occur (open full item for complete abstract)

Committee: Mohit Randeria (Advisor); Ilya Gruzberg (Committee Member); Thomas Lemberger (Committee Member); Yuri Kovchegov (Committee Member) Subjects: Physics

PHD, Kent State University, 2020, College of Arts and Sciences / Department of Physics

Condensed Matter Physics studies the states of matter in solids. Perhaps one of the most interesting physical phenomena are realized when materials are cooled down to very low temperatures, so that the principles of quantum mechanics together with the inter-particle correlations lead to the emergence of novel states of matter. In my work, I have successfully used the methods of Quantum Field Theory and Computational Physics to study and predict the novel phases of strongly correlated fermionic systems. In particular, I have explored the emergence of temporal and spatial phases in quantum mechanical systems ranging from degenerate atomic condensates to iron-based superconductors at very low temperatures. In this document, I will provide the details of my work with the specific examples of the fascinating problem of superfluid order parameter dynamics in fermionic condensates driven out-of-equilibrium, spatial phases in novel superfluids, and calculations of Josephson's interface between two iron-based superconductors.

Committee: Maxim Dzero (Advisor) Subjects: Condensed Matter Physics

MS, University of Cincinnati, 2024, Engineering and Applied Science: Materials Science

Refractory complex concentrated alloys (RCCAs) are known for their high-temperature mechanical properties, but less attention has been given to their low-temperature thermophysical behavior. High-throughput calculation of phase diagrams (CALPHAD) was used to study the body centered cubic (BCC) phase dominance within the Nbx(MoTi2V4)100-x alloy system by adding Niobium (Nb) at atomic concentrations of x=9%,23%,and 37%, and two additional alloys where vanadium (V) is substituted with hafnium (Hf) and zirconium (Zr) to form Hf10Mo24Nb38Ti28 and Mo24Nb38Ti28Zr10 alloys. Alloys were tested to see the effect of Nb content on the superconducting transition temperature (TC) and the effect of substituting V with Hf or Zr on TC. This approach tests the common assumption of the correlation between VEC with TC, to clarify the role of composition relative to VEC. Button specimens were cast via vacuum arc melting and were measured for electrical resistivity at different temperatures using a Quantum Design DynaCool system. X-ray diffraction (XRD) was used to confirm the formation of the phases predicted by CALPHAD. Five out of the six alloy samples exhibited superconductivity, with some anomalies observed and addressed in this study. These results are compared to literature to enhance understanding of the results.

Committee: Eric Payton Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Construction of future particle accelerators beyond the Large Hadron Collider will require high-field magnets which exceed the capability of current superconducting materials. Two superconductors exist today which can be produced in a multi-filament round wire form to construct magnets which generate 16-20 T: Nb3Sn which has been internally oxidized to produce oxide nanoparticles which function as artificial flux pinning centers (“APC Nb3Sn”), and Bi2Sr2CaCu2Ox (“Bi-2212”). These materials differ in many respects, including their basic structure and properties, the flux pinning mechanism that gives rise to their high values of critical current (Jc), and their magnetization behavior. In order to construct large-scale magnets from these materials, questions related to the formation and behavior of these materials must be resolved. In the case of Bi-2212, processing improvements have driven the Jc so high as to be strongly competitive with Nb3Sn, especially at higher magnetic fields. However, field errors (due to magnetization) and field drift (due to flux creep) still affect the design and quality of magnets made of Bi-2212. A Hall sensor and vibrating sample magnetometer were used to measure the magnetization response to various field sweep cycles of a segment of Bi-2212 cable and several miniature coils of the strand from which the cable was made. To examine the temporal decay of magnetization due to flux creep, the sample was exposed to a series of field sweeps, meant to simulate the pre-injection field sequence in a particle accelerator, of the form 0 T, 2.5 T, μ0Hpreinj, 1 T, where μ0Hpreinj is each of several values between -1 T and 1 T. It was found that the rate of decay of the examined Bi-2212 sample is independent of deformations and cabling. In the case of Nb3Sn, significant improvement has been made to the critical current density (Jc) by the introduction of oxide nanoparticles. These non-superconducting particles add an additional point-based flux (open full item for complete abstract)

Committee: Michael Sumption (Advisor); Tyler Grassman (Committee Member); Sheikh Akbar (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Rare-earth barium copper oxide (REBCO) coated conductors (CCs) are of interest for fabricating high-performance cables and magnets for high-field applications (B > 22.5 T). However, the applications of REBCO CCs are facing some critical challenges, such as quench detection and protection, high magnetization loss and magnetization creep, and flux jumping due to thermal instability. Because it is inevitable to introduce defects in REBCO CCs during the processes of manufacturing, cabling, and winding, it is important to control the current sharing between conductor tapes to enable the self-protection mechanism to take place when a localized disturbance (hot spot) appears in the cable or magnet coil. The current sharing between conductor tapes can be modified by changing inter-tape surface contact. Our study found that inter-strand contact resistance (ICR) and inter-strand thermal resistance (ITR) are determinant factors for current sharing. We modified the inter-strand contact surface properties by applying different techniques. By applying pressure, cold pressing and hot pressing, the inter-strand electrical contact efficiency, η (η = ICR ∗ contact area) can be reduced to as low as 10 µΩ*cm2, at which value effective current sharing between REBCO CC tapes can be achieved. However, applying compression is only feasible for tape stack structure where tapes directly lay above one another without any twist pitch. For cables, such as Roebel cable, CORC cable, and STAR cable, the compression limits are much lower than that of the tape stack. Applying pressure can easily damage the tapes in the cables, leading to reduction of Ic. Therefore, performing Ni-plating and PANI coating are more suitable options. The inter-strand electrical contact efficiency, η, achieved by Ni-plate technique is 2.7 µΩ*cm2. PANI-coating offers a wide range of η-values needed for different requirements of various applications. We applied experimentally achieved inter-strand contact properties to (open full item for complete abstract)

Committee: Michael Sumption (Advisor); Jinwoo Hwang (Committee Member); Sheikh Akbar (Committee Member) Subjects: Materials Science

PHD, Kent State University, 2023, College of Arts and Sciences / Department of Physics

Nonlinear optics has been a fascinating area of research for many years. Most recently nonlinear optical effects such as photovoltaic and photogalvanic effects became an active topic of research in the context of the recently discovered monochalcogenides. Group IV monochalcogenides monolayers (MMs) (GeS, GeSe, SnS and SnSe) are a special class of 2D materials which are of interest to researchers due to their tunability, large values of electronic mobility as well as high potential for optoelectronic applications. Those materials behave as 2D ferroelectrics, display bulk photovoltaic effect and serve as a platform to study relation between dimensionality and spontaneous polarization. Another class of advanced quantum materials – heavy-fermions – serve as a playground to study competing many-body ground states, such as superconductivity and magnetism. Most recently, some heavy-fermion systems, such as samarium hexaboride, have been predicted to exhibit a topologically nontrivial ground state, which lead to a flurry of experimental and theoretical activities. We studied the second harmonic generation (SHG) and injection current in MMs employing density functional theory (DFT) and validated the data through tight binding model. We showed that the JDOS, alone, cannot explain injection current in MMs but rather a combination of factors including, in-plane polarization, reduced dimensionality, anisotropy, and covalent bonding all of which are closely intertwined. I have also studied how the electron-electron interactions affect thermodynamic properties of Sm based and Ce-based heavy-fermion systems. Our work has been motivated by recent discovery of the Ce-based cage compounds CeNi2Cd20 and CePd2Cd20 which have vanishing RKKY interactions and do not exhibit a long-range order down to very low temperatures in the millikelvin range. We propose that d-wave superconductivity may develop in these compounds under an application of the hydrostatic pressure.

Committee: Maxim Dzero (Advisor); Benjamin Fregoso (Advisor); Artem Zvavitch (Committee Member); Gokarna Sharma (Committee Member); Almut Schroeder (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2022, Physics

The thesis deals with three fundamental problems lying at the intersection of correlations and topology in quantum materials. They are further divided into two broad classes: superconductivity in strongly correlated systems and Hall effect in chiral magnets. The first questions what material parameters control the superconducting (SC) transition temperature $T_c$. In many novel superconductors, SC phase fluctuations determine $T_c$, rather than the collapse of the pairing amplitude. We derive rigorous upper bounds on the superfluid phase stiffness for multi-band systems, valid in any dimension. This in turn leads to an upper bound on $T_c$ in two dimensions (2D), which holds irrespective of mechanism, pairing interaction strength, or order-parameter symmetry. We first show that $k_BT_c \leq E_F/8$ for a single parabolic band in 2D with Fermi energy $E_F$, a result that has direct implications for systems as diverse as Li-doped ZrNCl and the 2D BCS-BEC crossover in ultra-cold Fermi gases. We further derive bounds on monolayer FeSe on STO and magic-angle twisted bilayer graphene (MA-TBG) using the available band structures. We then discuss the question of deriving rigorous upper bounds on $T_c$ in 3D. In the second project, we present exact results that give insight into how interactions lead to transport and superconductivity in a flat band where the electrons have no kinetic energy. We obtain bounds for the optical spectral weight for flat band superconductors. We focus on on-site attraction $|U|$ on the Lieb lattice with trivial flat bands and on the $\pi$-flux model with topological flat bands. For trivial flat bands, the low-energy optical spectral weight $\widetilde{D}_\text{low} \leq \widetilde{n} |U| \Omega/2$ with $\widetilde{n} = \min\left(n,2-n\right)$, where $n$ is the flat band density and $\Omega$ the Marzari-Vanderbilt spread of the Wannier functions (WFs). We also obtain a lower bound involving the quantum metric. For topological flat bands, wit (open full item for complete abstract)

Committee: Mohit Randeria (Advisor); Christopher Hirata (Committee Member); Fengyuan Yang (Committee Member); Yuan-Ming Lu (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2021, Physics

Two-dimensional crystals have become a prominent part of condensed-matter research for many years due to the unique adaptability of their interlayer interactions. This ability to isolate and stack individual crystal layers has led to the exploration of low dimensional physics and has spurred the creation of countless van der Waals heterostructure devices. Graphene, a monolayer of graphite, has spearheaded this research and continued to remain at the forefront since the tremendous activity directed towards it following the experiment of 2004 [1]. More recently, graphene has regained the spotlight with the discovery of twisted bilayer graphene, a heterostructure consisting of two overlapping graphene layers with an interlayer twist. As a result of the twist, a geometric interference pattern whose periodicity can be controlled by the relative angular alignment between them is formed. This is known as a moire pattern and it creates a superlattice potential that modifies the electronic structure of the system. For twist angles of about 1.1°, the “magic angle”, flat bands form near zero Fermi energy, resulting in a number of correlated phases including Mott-like insulators, superconductivity, and magnetism. [2-12] Another atomically thin two-dimensional material of interest is black phosphorus (BP), a semiconductor with high electron mobility and a tunable direct band gap. BP is an allotrope of phosphorus that can be obtained by heating up white phosphorus under high pressure. Known as phosphorene when it is mono- or few-layered, BP possesses an anisotropic crystal structure, which translates to anisotropic electronic, optical, and thermal properties [13, 14]. As a result of these particularly interesting features, phosphorene has spurred its own set of studies [15-26] The focus of this dissertation can be divided into two parts. In the first part (Chapters 1-6), it will explore Hall transport in TBG near the magic angle [27]. In the second part (Chapters (open full item for complete abstract)

Committee: Marc Bockrath (Advisor); Chun Ning Lau (Committee Member); Ilya Gruzberg (Committee Member); Richard Furnstahl (Committee Member) Subjects: Materials Science; Physics

PHD, Kent State University, 2021, College of Arts and Sciences / Department of Physics

Strongly correlated electron systems constitute a rich reservoir for interesting physical phenomena. The competition and interplay between the localized magnetic moments in partially filled d or f electron systems and the itinerant conduction electrons states lead to novel phenomena such as complex magnetic properties, unconventional superconductivity, non-Fermi-liquid behavior, and the coexistence of superconductivity and magnetism. Such intriguing physical phenomena can be achieved by tuning the system with a control parameter, such as chemical composition, applied pressure, and magnetic field. It is interesting to study the chemical substitution effects on the correlated f electron system along with magnetic field to explore their complex phase diagram. This dissertation work focuses on experimental studies of the Ce and Eu substituted filled skutterudite system PrPt4Ge12 over a wide range of doping, magnetic field, and temperature using heat capacity measurements. The first study will focus on the specific heat and electrical resistivity measurements performed on the Pr1-xCexPt4Ge12 crystals. We have found that Ce monotonically suppresses the superconducting transition temperature Tc and a small Ce concentration of x = 0.14 brings the Tc to as low as 0.6 K. We further have demonstrate that small Ce substitution does not affect the multiband nature of superconductivity seen previously in the parent compound PrPt4Ge12. On the other hand, our data provide evidence that one of the two gaps is nodal in the parent compound and that Ce substitution gradually suppresses the value of the nodal gap. To understand the possible interplay between superconductivity and magnetism, we study the same parent system PrPt4Ge12, this time substituting Pr with europium. The compound so formed is Pr1-xEuxPt4Ge12 whose end members are superconductor (x = 0) and antiferromagnetic (x = 1) at lower temperatures, so that there is the possibility of interaction between super (open full item for complete abstract)

Committee: Carmen Almasan (Advisor); Maxim Dzero (Committee Member); Almut Schroeder (Committee Member); Mietek Jaroniec (Committee Member); Songping Huang (Committee Member) Subjects: Physics

Master of Science, Miami University, 2019, Physics

The superconducting properties of a series of Ni2ZrAl1-xGax, Ni2ZrAl1-xBx and Ni2-xCuxZrGa Heusler compounds have been explored via x-ray diffraction, scanning electron microscopy, electrical resistivity, dc magnetization, and ac susceptibility measurements. In common, all samples exhibited the cubic L21cubic structure at room temperature. For x ≥ 0.20, the Ni2ZrAl1-xBx compounds exhibited multiple phase, swerving away from the single cubic phase of the parent compound, Ni2ZrAl. All Ga doped compounds, evinced superconductivity with superconducting transition temperature, Tc, increasing with higher Ga doping while the TC of the Ni2ZrAl1-xBx compounds marginally decreased from ~ 2.2 K (x = 0) to ~ 2.0 K (x = 0.15). The Tc of 2.2 K observed for Ni2ZrAl is significantly larger than the reported value of 1.38 K. For all Cu-doped compounds, Tc decreased with increase in Cu concentration and application of magnetic field. This decrease in TC is indicative of the phase transition that occurs near zero Kelvin, quantum phase transition. The dc magnetization data suggested the type-II superconductivity for all the compounds. The experimental results with related discussion is presented in detail.

Committee: Mahmud Khan (Advisor); Herbert Jaeger (Committee Member); Samir Bali (Committee Member) Subjects: Physics

Doctor of Philosophy (PhD), Ohio University, 2019, Physics and Astronomy (Arts and Sciences)

The work presented in this dissertation is concerned with properties of nuclei, their internal constituents, nucleons and quarks, of which nucleons are made, in the astrophysical settings of nucleosynthesis, core-collapse supernovae, neutron stars and their mergers. Through energetic considerations, nuclei far-off the stability line are expected to be encountered in all of the arenas mentioned above. Properties of some of these nuclei are expected to be measured in upcoming rare-isotope laboratories across the world. Focussing on the pairing properties of extremely proton- or neutron-rich nuclei, a means to set bounds on their pairing energies was devised in the published work reported here. These bounds were achieved through the introduction of a new model, the Random Spacing Model, in which single-particle energy levels randomly distributed around the Fermi surface of a nucleus were employed. This arrangement ensured that it would encompass predictions of all possible energy density functionals currently being employed. Another new feature of this model is the inclusion of pairing gap fluctuations that go beyond the commonly used mean field approach of determining pairing energies of nuclei. These features, when combined together, enabled us to reproduce the S-shaped behavior of the heat capacity measured in laboratory nuclei. In future work, nuclear level densities, which depend sensitively on pairing energies at low excitation energies, will be calculated using the Random Spacing Model with the inclusion of pairing fluctuations. For baryon densities below about two thirds the central density of heavy nuclei, a mixture of light nuclear clusters such as ${\rm \alpha}$, ${\rm d}$, ${\rm t}$, etc., are favored to be present along with nucleons (neutrons and protons), charge balancing electrons, and heavy nuclei. The concentration of each species is determined by minimizing the free energy density of the system with respect to baryon density, electron fra (open full item for complete abstract)

Committee: Madappa Prakash (Advisor); Zach Meisel (Committee Member); Steven Grimes (Committee Member) Subjects: Astrophysics; Nuclear Physics; Physics; Theoretical Physics

Doctor of Philosophy, The Ohio State University, 2019, Physics

Superconductivity has been at the heart of research into quantum phenomena since its discovery over a century ago. More recently efforts have been made to understand the nature of the quantum phase transition (QPT) that separates the superconducting and insulating phases in certain 2D materials at zero temperature. This superconductor-insulator transition (SIT) has been theoretically and experimentally proven to be driven by quantum fluctuations of the superconducting phase instead of the breakup of Cooper pairs. In this thesis we present a study of quantum fluctuations across the SIT and how they can be imaged in both theoretical simulations and experimental measurements. We begin with an overview of the field from a historical perspective, describing the development of the theory of SITs driven by experiments on thin films. We present the Josephson junction array (JJA) model as a paradigm to investigate the quantum phase fluctuation-driven SIT using quantum Monte Carlo (QMC) techniques. We explore the manifestation of quantum fluctuations across the SIT in three different local measurements: the diamagnetic susceptibility χ(r), two-particle density of states P(r, ω), and compressibility κ(r), revealed through their local maps and calculated via QMC. χ(r) probes the system's ability to generate diamagnetic currents and its local map displays growing fluctuations upon increasing both temperature the quantum tuning parameter g. Remarkably, however, these fluctuations persist well below Tc as the SIT is approached, indicating the quantum nature of these fluctuations. We compare our results to SQUID susceptometry measurements performed on thin-film NbTiN and find good qualitative agreement. The map of κ(r) paints a similar picture when tuned via g, but in contrast to χ(r), we find a fundamental difference in its evolution with temperature, providing a complementary local probe to χ(r). P(r, ω), obtained using Maximum Entropy analytic continuation of imaginary time Q (open full item for complete abstract)

Committee: Nandini Trivedi (Advisor); Yuan-Ming Lu (Committee Member); Rolando Valdes-Aguilar (Committee Member); Richard Furnstahl (Committee Member) Subjects: Physics; Theoretical Physics

Master of Science, Miami University, 2018, Physics

The superconducting properties of a series of ZrNi2-xTMxGa (TM = Cu, Co) and ZrNi2AlxGa1-x Heusler compounds have been explored by x-ray diffraction, scanning electron microscopy, electrical resistivity, dc magnetization and ac susceptibility measurements. In common, all samples exhibited the cubic L21 Heusler structure at room temperature. For x = 0.25, the ZrNi2-xCuxGa compounds demonstrated superconductivity and the superconducting transition temperature, TC, decreased with increasing Cu concentration. The dc magnetization data suggested the type-II superconductivity for all the Cu-doped compounds. Unlike ZrNi2-xCuxGa, up to the lowest measuring temperature of 1.75 K, no superconductivity was observed in any of the ZrNi2-xCoxGa compounds. All the Al-doped compounds also showed type-II superconductivity with a decrease in Tc. In addition, the ZrNi2AlxGa1-x compounds showed a new phase transition a few kelvins above superconducting transition. The experimental results are presented and discussed in detail.

Committee: Mahmud Khan Dr. (Advisor); Herbert Jaeger Dr. (Committee Member); Khalid Eid Dr. (Committee Member) Subjects: Physics

Master of Science, Miami University, 2017, Physics

The superconducting and magnetic properties of a series of Zr1+xNi2-xGa and Zr1-xNi2+xGa compounds have been investigated by x-ray diffraction, scanning electron microscope, electrical resistivity, dc magnetization, and ac susceptibility measurements. Van hove singularity, which refers to a high density of states near the fermi energy level, are believed to cause superconductivity in these materials. The electron concentration is less than 6.5 in Zr1+xNi2-xGa compounds while greater than 6.5 in Zr1-xNi2+xGa compounds. While the parent compound, ZrNi2Ga, exhibited the cubic L21 Heusler structure, multiple non-cubic structures of tetragonal and monoclinic phases formed in the doped Zr1+xNi2-xGa and Zr1-xNi2+xGa materials. For x > 0.3, the Zr1+xNi2-xGa compounds show structural order of dominant monoclinic phase with a small presence of the tetragonal phase. On the other hand, the Zr1-xNi2+xGa compounds show structural disorder of cubic, tetragonal, and monoclinic phases. For x = 0.3, all Zr1-xNi2+xGa compounds demonstrated superconducting behavior, but no superconductivity was observed in the Zr1+xNi2-xGa alloys for x > 0.2. The magnetization data revealed that all materials in both the Zr1+xNi2-xGa and Zr1-xNi2+xGa series exhibited type-II superconductivity. With increasing doping concentration x, the paramagnetic ordering was enhanced in both systems while the superconducting properties were found to weaken. The observations are discussed considering the structural disorders in the systems.

Committee: Mahmud Khan (Advisor); Khalid Eid (Committee Member); Herbert Jaeger (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2002, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering

Magnesium diboride (MgB2) is a material with a superconducting transition temperature of 39 K. Discovered in 2001, the relatively large coherence length (and associated lack of weak links) together with its simple binary composition (making phase pure formation relatively easy) have made it a material of substantial interest. However, its inadequate in-field performance limits the high field applications. Chemical doping is the key to increasing the Bc2 of MgB2. Chemical doping aiming at Mg site or B site substitution is of interest and both routes are explored in this thesis. Structure-property correlations are developed for dopants that either do or do not, incorporate themselves into the MgB2 matrix. First, the effects of C doping in the state of art MgB2 wires were investigated. In order to do so, a series of state of the art C doped MgB2 wires, in both mono-filamentary and multi-filamentary forms, were fabricated by a local company. Their transport and magnetic performance in various magnetic fields, and mechanical induced degradation, were examined. The C doping influence on the critical current density and the n-values were discussed. Secondly, the effects of rare earth oxide (REO) doping in MgB2 were studied. Two sets of samples including both bulk samples and wires were fabricated. Microstructural evidence obtained by SEM and TEM proved that nano-size inclusions formed after REO doping acted as grain growth inhibitors, as evidenced a reduction of MgB2 grain size in REO doped bulk samples. The results of XRD and magnetic measurements on the bulk samples demonstrated that Dy2O3 and Nd2O3 do not alloy with MgB2, no changes being observed in the lattice parameters, Tc and Bc2 of doped MgB2. Enhancements in flux pinning and Jc were obtained in both bulk samples and wires by REO doping, consistent with the microstructural evidence of notable grain refinements and the presence of nano-size inclusions as new pinning sites in MgB2 grains. Lastly, a set of metal d (open full item for complete abstract)

Committee: Michael Sumption (Advisor); Patricia Morris (Committee Member); Roberto Myers (Committee Member) Subjects: Electromagnetics; Electromagnetism; Engineering; Materials Science; Metallurgy; Physics

MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering

This thesis concentrates on developing an innovative method to generate thrust force for spacecraft in localized geomagnetic fields by various electromagnetic systems. The proposed electromagnetic propulsion system is an electromagnet, like normal or superconducting solenoid, having its own magnetic field which interacts with the planet's magnetic field to produce a reaction thrust force. The practicality of the system is checked by performing simulations in order the find the varying radius, velocity, and acceleration changes. The advantages, challenges, various optimization techniques, and viability of such a propulsion system in present day and future are discussed. The propulsion system such developed is comparable to modern MPD Thrusters and electric engines, and has various applications like spacecraft propulsion, orbit transfer and stationkeeping.

Committee: Grant Schaffner Ph.D. (Committee Chair); George T Black M.S. (Committee Member); Kelly Cohen Ph.D. (Committee Member) Subjects: Aerospace Materials