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Thesis advisor: Michael J. Graf / Quantum spin liquids (QSL)’s have been one of the most hotly researched areas ofcondensed matter physics for the past decade. Yet, science has yet to unconditionally identify any one system as harboring a QSL state. This is because QSL’s are largely defined as systems whose electronic spins do not undergo a thermodynamic transition as T→0. Quantum spin liquids remain fully paramagnetic, including dynamical spin fluctuations, at T=0. As a result, distinguishing a QSL system from a conventionally disordered system remains an outstanding challenge. If a system spin freezes or magnetically orders, it cannot be a QSL. In this thesis I present published experiments I have performed on QSL candidate materials. By using muon spin rotation (μSR) and AC magnetic susceptibility I have evaluated the ground states of several candidates for the absence of long-range magnetic disorder and low-temperature spin-fluctuations. For the systems which order or spin-freeze, my research provided key knowledge to the field of frustrated magnetism. The systems I studied are as follows: The geometrically frustrated systems NaYbO2 and LiYbO2; the Kitaev honeycomb systems Cu2IrO3 and Ag3LiIr2O6; and the metallic kagome system KV3Sb5. Each of these systems brought new physics to the field of frustrated magnetism. NaYbO2 is a promising QSL candidate. LiYbO2 harbors an usual form of spiral incommensurate order that has a staggered transition. Cu2IrO3 has charge state disorder that results in a magnetically inhonogenious state. Ag3LiIr2O6 illustrates the role structural disorder plays in disguising long-range magnetic order. And finally, KV3Sb5 isn’t conventionally magnetic at all; our measurements ruled out ionic magnetism and uncovered a type-II superconductor. Our measurements on KV3Sb5 stimulated further research into KV3Sb5 and it’s unconventional electronic states. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

PhD Thesis / The superconductivity in heavy-fermion compounds, iron pnictides and cuprates has been intensively studied for over thirty years. Amongst some of these materials, the common denominator is the presence of strong antiferromagnetic fluctuations in their normal state, signaling an underlying quantum phase transition between a paramagnetic metal and a metal with antiferromagnetic long-range order. Although the quantum critical point is experimentally inaccessible due to the presence of superconducting order, it determines the physical properties of the normal state of the metal in a wide range of temperatures. In this thesis we study the low-energy theory for the critical metallic state that arises at the aforementioned quantum critical point. We present a nonperturbative study of the theory in spatial dimensions between two and three. We pay special attention to two dimensions where we show that our physical predictions are in qualitative agreement with experiments in electron-doped cuprates. We further develop a field theoretic functional renormalization group scheme that is analytically tractable. It provides a general framework to study the low-energy theory of metallic states with or without a quasiparticle description. Within this formalism we characterize the single-particle properties of the antiferromagnetic quantum critical metal. This allows one to study the superconducting instability triggered by critical antiferromagnetic quantum fluctuations quantitatively. / Thesis / Doctor of Science (PhD)

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Between 4-16% of adults in the United States have experienced difficulty swallowing at some point during their lives. Difficulty swallowing, or clinically referred to as dysphagia, poses increased concern when drinking beverages. While no treatment is currently available, it is often recommended that liquids be thickened to improve the safety of swallowing and prevent liquids from being aspirated in the lungs. However, thickened liquids are poorly accepted by individuals with dysphagia. Taste and flavor suppression has been shown in various thickened liquid matrices, but the mechanisms for understanding these changes in perception are quite complex. Additionally, literature focused on dysphagic patients’ experiences with different types of beverages and clinicians’ experiences with thickening beverages is minimal. The study had two main goals: 1) explore how sensory properties including texture, taste, and flavor affect acceptance of specific thickened liquids and 2) determine challenges clinicians experience with thickening different beverages. This was achieved through a quantitative and qualitative online survey administered to clinicians (n=83; 96% speech-language pathologist) in the United States who work with dysphagia patients. Free-response questions related to thickening issues highlighted challenges with carbonation, temperature, and dairy products. Coffee, water, soda, milk, and oral nutritional supplements were the most complained about thickened beverages, respectively. Disliking of texture was a common complaint for each beverage likely due to the dissimilarity to the unthickened version and challenges associated with thickening. Off-flavors were reported for each beverage and were the most present in water. Additionally, clinicians noted the thickened version of the beverage typically has less flavor. To increase the acceptance of thickened liquids, clinicians believe the texture and flavor need significant improvements. Interdisciplinary work in the field of food science is needed to create a smoother consistency, more stable thickness across time and temperature, and improved flavor/taste to develop more enjoyable beverages for dysphagic patients.

Rare earth elements (REE) exhibit particular and unique properties that render them essential to technological applications. Of particular interest is their involvement in the transition toward global sustainability and their military applications. The magnetic properties of the rare earth elements is of primordial importance to sustainable development. More specifically, terbium and dysprosium are two elements with no known substitutes in critical applications and with no domestic or allied sourcing available. These elements are currently mined by in-situ leaching of ion-absorbed clays, mostly from illegal operations in Myanmar financed by Chinese companies. The demand from both elements, and for the other magnet rare earths is projected to growth at very high rates through 2035 while the world undergoes a transition toward sustainability, and a drastic reduction in greenhouse gases emissions. Our team has been evaluating the potential of acid mine drainage (AMD) as a source of rare earth elements and critical materials (CM). Acid mine drainage is the result of in-situ generation of sulfuric acid due to the weathering of sulfide ores. It is a significant legacy environmental issue and one of the largest pollutants in many mining districts throughout the world. The objective of the present work is to provides a roadmap for the utilization of AMD as a critical material feedstock to preserve the independence of the United States of America with regards to these materials. To that effect, a fundamental economic assessment of REE/CM recovery from AMD using a network sourcing strategy in addition to a robust, flexible feedstock separations and refining facility was undertaken. A techno-economic analysis of the extraction, refining, separation and reduction to metal is presented along with a sensitivity analysis.The results of this analysis show that, with the exception of the minimum price scenario, all operational configurations have positive economic indicators with rates of return varying from 25% to 32% for the contemporary price scenario. This is primarily due to the very high enrichment in terbium and dysprosium of AMD. The optimal configuration was determined to be production of Co, Mn, and all REEs except for mischmetal, which is not recovered. Sensitivity analysis and Monte Carlo Simulation show that capital cost and HCl consumption are the two major factors influencing rate of return, thus indicating opportunities for future technology development and cost optimization. In order to reduce both the capital and operation cost of the facility, alternative ionic liquids extractants based on conventional acidic extractants where synthesized and investigated. The results show that the ionic liquids varied in performance, with [c101][D2EHP] and [c101][EHEHP] performing poorer than their conventional counterparts and [c101][c572] performing better. The performance of [c101][c572] was 13% superior to Cyanex 572, 20% superior to EHEHPA and 27% superior to D2EHPA the current commercially used extractants. Recommendations for further study on [c101][c572] include stripping tests, continuous pilot testing, and techno-economic analysis. The test work revealed that zinc and to a lesser extent calcium were significant deleterious elements in the solvent extraction circuit, and that selective removal would significantly reduce the acid-base consumption of the separation circuit. A process was developed to selectively remove calcium and zinc from AMD-derived feedstock and from REE products. The ammonium chloride leach process offer many advantages, including the possibility of closing the cycle by using carbon dioxide sequestration as a step to regenerate the ammonium chloride in a zero-discharge process. / Doctor of Philosophy / A younger me: - What are these elements in the bottom of the periodic table? My high school chemistry teacher: - "Don't waste time there, these are of no concern." Twenty years later, technological developments and the imperative to transition away from fossil energy to mitigate climate change have brought the rare earth elements, a series of 17 elements with unique properties to the forefront of the conversation. In addition to an organic increase in demand, the recent supply chain consolidation by China is adding a geopolitical risk to the equation. The magnetic properties of the rare earth elements is of primordial importance to sustainable development and to our military technology. More specifically, terbium and dysprosium are two elements with no known substitutes in critical applications and with no domestic or allied sourcing available. These elements are currently mined from illegal operations in Myanmar, with the support of Chinese companies. The demand from both elements, and for the other magnet rare earths is projected to growth at very high rates through 2035 while the world undergoes a transition toward sustainability, and a drastic reduction in greenhouse gases emissions. Given the important of the rare earth elements, and the absence of significant deposits in the united states, with the exception of the Bear Lodge and Elk Creek deposits, the Department of Energy has mandated academic institution of evaluating alternative sources of rare earth elements. Our team has been evaluating the potential of acid mine drainage as a source of rare earth elements and critical materials. Our team has surveyed many acid mine drainage sources and determined that many sites are highly enriched in terbium and dysprosium. Acid mine drainage is a legacy environmental issue related to past problematic mine development techniques. In the problematic mines. these acidic mine waters are permanently generated and if not treated can have severe impacts on water streams in which they flow. The toxicity of the acid mine drainage on the environment is due to its high acidity and significant levels of toxic metals. Acid mine drainage can be recognized by their yellow to red tint. It is treated by reacting it with a neutralization agent, which results in treated water and a sludge. The sludge is dewatered and stored in tailing impoundments. I have designed a process for the economical recovery of rare earth elements and critical materials from acid mine drainage. The cost to build and operate the facility was derived and it was determined that the project could be further enhanced by reducing the plant chemical reagent consumption. One specific category of chemical referred to as extractant, is central to the rare earth separation process. A novel variation on the standard extractants has been evaluated and promises to provide significant savings. While the extractants were investigated, it was noticed that some impurities such as zinc and calcium created issues in the circuit. I then developed a process for their selective removal. The process also provide a net carbon dioxide sequestration potential.