Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 107-116).

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 79-83).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

Quantum materials are solids that have unique electronic, magnetic, or optical properties arising due to quantum mechanical effects. Superconductors, topological insulators, and exotic magnets are examples of quantum materials. This thesis comprises three studies that explore the properties of four superconductors and a breathing pyrochlore magnet. In the first study, we investigate the superconducting properties of Re3B, and Re7B3 and determine the role of Re concentration and crystal inversion symmetry. Our findings reveal conventional superconductivity in both of these superconductors, despite having many ingredients for hosting unconventional superconductivity. The second study investigates the superconducting properties of non-centrosymmetric superconductors TaRuSi and TaReSi, specifically focusing on the role of spin-orbit coupling. By using density functional theory calculations, we determine the magnitude of anti-symmetric spin-orbit coupling and, using a combination of zero field and transverse field muon spin rotation /relaxation, reveal that TaRuSi hosts an unconventional superconducting state with broken time-reversal symmetry. TaReSi, however, hosts a conventional superconducting state. In the third study, we describe the synthesis and physical and magnetic properties of CuAlCr4S8, which is a breathing pyrochlore magnet. Breathing pyrochlores consist of a three-dimensional array of corner-sharing tetrahedra of alternating size formed by magnetic atoms, and their magnetic properties can be tuned by adjusting the breathing ratio. We demonstrate how CuAlCr4S8 allows for the clean realization of breathing pyrochlore physics, due to the absence of any structural transition. Overall, our studies contribute to a deeper understanding of the properties of unconventional superconductors and breathing pyrochlore magnets, revealing new insights into their exotic physics and the underlying mechanisms that govern their behaviors. / Thesis / Candidate in Philosophy / We study superconducting Re3B, Re7B3, TaRuSi, and TaReSi to understand the role of symmetries of the crystal structure and spin-orbital coupling in generating unconventional superconducting properties. We learn that Re3B, Re7B3, and TaReSi display conventional superconducting properties, whereas TaRuSi exhibits unconventional superconducting behavior in the form of time-reversal symmetry-breaking fields and a nodal superconducting gap. A breathing pyrochlore consists of magnetic atoms at the vertices of corner-sharing tetrahedra of alternating sizes. We synthesized a new Cr-based breathing pyrochlore magnet, CuAlCr4S8, and studied its physical and magnetic properties. The ratio of sizes of two tetrahedra in CuAlCr4S8 is 1.0663(8), and it undergoes an antiferromagnetic transition of a purely magnetic nature at 20 K. We conclude that CuAlCr4S8 is an ideal system to study breathing pyrochlore physics due to low anti-site disorder.

Superconductivity has been a topical dicovery of materials research and condensed matter physics since its discovery in 1911. It has seen applications appear within cutting edge technology, yet the mechanism for this exotic quantum phenomena remains unclear. This thesis is centred on the preliminary study on one family of the cuprate high Tc superconductors, the La1.6−xNd0.4SrxCuO4 (Nd-LSCO) system. We were able to synthesize single phase polycrystalline material of Nd-LSCO across its phase diagram from x 0.02 to x 0.4. We were also able to grown three large, high quality single crystal samples of this system at high doping, for the first time. Large single crystals of La1.6−xNd0.4SrxCuO4 (x=0.17, 0.19 and 0.24) were successfully grown using the traveling solvent floating zone technique. This thesis focuses on an introduction to the relevant materials preparation and crystal growth techniques and a discussion of some of the characterization of the samples which necessarily is involved in such a systematic study. / Thesis / Master of Science (MSc)

Although charge order was discovered in \lndsco over two decades ago, this elusive state has not been as easily observable in \lsco. \cu NMR experiments demonstrated that \lsco did indeed transition into a charge ordering state, but the lack of evidence in other experiments made many physicists doubtful of its presence. With recent advancements in technology, x-ray scattering experiments have finally been able to measure charge order Bragg peaks in \lsco, proving that charge order anomalies seen by \cu NMR was legitimate. More recent \cu NMR showed that a broad wing-like signal emerges when charge order sets in in \lscoeleven with a much faster relaxation rate than the normal signal. In this thesis, we attempt to revisit the charge ordered state of \lsco by measuring \la NMR on single crystals of x~=~0.13, 0.115 and 0.10. By splitting the relaxation rate into two components, we were able to determine the temperature at which a fast component emerges, corresponding to the same temperature recorded by \cu NMR and x-ray scattering for the same \lscoeleven crystal. Using this method, we measured \la NMR lineshapes and spin-lattice relaxation rates and mapped out the charge order dome of the phase diagram of \lsco. / Thesis / Master of Science (MSc)

Methods of processing large grained textured superconductor have been successfully developed, based on a melt texturing process. Large grained textured superconductor with grain size over 10mm along the growth direction and Jc over 3600A/cm² (77K, 0.5 Tesla) has been produced in both one - zone and two - zone furnaces with good reproducibility. Two kinds of design of reactive metal contacts have been proposed and investigated, aiming to make low resistivity contacts with strong mechanical strength. Three possible reactive contact metals have been tested for contact making, and the microstructures at the interfaces have been studied to find the relations between contact resistivity and contact processing conditions. Titanium/noble metal multilayer contacts is a promising type of contact technique for low resistivity and strong mechanical bonds. Gold and silver contacts give resistivities among the best reported results in the literature, and they turned out to be extremely stable in time, could withstand repeated thermal cycling from room temperature to 10K and yield very reproducible R-T curves. The electrochemical titration method has been used to increase the oxygen stoichiometry of bulk textured YBa₂Cu₃O_7-x samples. The electrochemical titration method can further oxidize melt textured thick film YBa₂Cu₃O_7-x samples in which it may be difficult to further improve oxygen content by conventional annealing. The solid state electrochemical cell has been used to study the thermodynamic properties of the Y-Ba-Cu-O system at high oxygen pressure by measuring the oxygen activity versus time continuously immediately after the electrochemical titration. A series of computer models have been set up according to the microstructure of the contact interface to simulate the complicated contact resistivity behaviours. The nature of, and geometry of, the reaction products at the contact interfaces may be revealed by the temperature dependence of the contact resistance. This information combined with direct observations on the structure and chemistry of the contacts provided a fuller understanding of conduction mechanism at the contact interface.

Thesis (Master)--İzmir Institute of Technology, İzmir, 2006 / Keywords: Superconductivity, bolometer. Includes bibliographical references (leaves. 74-78).

<p>Scientific progress often relies on unexpected discoveries and unique observations. In</p> <p>fact, many of the most groundbreaking scientific advances throughout history have been the</p> <p>result of serendipitous events. For instance, the discovery of penicillin by Alexander Fleming</p> <p>was a result of him noticing a mold growing on a petri dish that was contaminating his</p> <p>bacterial culture. Similarly, the discovery of the cosmic microwave background radiation,</p> <p>which is considered one of the strongest pieces of evidence for the Big Bang theory, was</p> <p>the result of two scientists accidentally stumbling upon it while conducting a completely</p> <p>different experiment. These types of unexpected discoveries can lead to new avenues of</p> <p>research and open up entirely new fields of study. During my PhD, I experienced a similar</p> <p>phenomenon when I stumbled upon an anomaly in my experimental data that led me down a</p> <p>completely new path of investigation. This unexpected discovery not only provided me with</p> <p>new insights into the underlying mechanisms of my research, but also opened new avenues for</p> <p>future research directions. It was a reminder that sometimes the greatest scientific progress</p> <p>can come from the most unexpected places.</p> <p>My primary focus was initially directed towards topological superconductivity. However,</p> <p>this research direction was modified by unexpected findings while characterizing a SQUID.</p> <p>Specifically, a unique response by a Josephson junction was observed when exposed to an inplane</p> <p>magnetic field. Chapter 1 details our experimental results on the SQUID. We observed</p> <p>intriguing effects resulting from the in-plane magnetic field in the asymmetric evolution of</p> <p>the Fraunhofer pattern suggesting the existence of additional underlying physics in the heterostructure,</p> <p>which may have been previously overlooked. This serendipitous finding served</p> <p>as the impetus to explore simpler superconducting devices such as nanowires and rings.</p> <p>Remarkably, subsequent investigations into the critical current of a superconducting ring revealed</p> <p>a bi-modal histogram arising from the application of an in-plane magnetic field, which</p> <p>was an unforeseen outcome. This adds to our observations made in chapter 1. Chapter 2 details</p> <p>the unique properties of Al-InAs superconducting rings. Further experiments involving</p> <p>a superconducting nanowire resulted in the observation of non-reciprocal critical current under</p> <p>an in-plane magnetic field perpendicular to the current direction, subsequently referred to as the superconducting diode effect. Chapter 3 delves into the non-reciprocal properties</p> <p>of an Al-InAs superconducting nanowire. Our findings revealed the diamagnetic source of</p> <p>non-reciprocity generic to multi-layer superconductors. Finally, chapter 4 provides a detailed</p> <p>account of the fabrication processes for the superconducting devices, along with a discussion</p> <p>of the measurement techniques employed to unveil the underlying physics.</p>