Ground States of Disordered Quantum Magnets

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****Technical Abstract****The aim of the proposed research is to obtain a deeper understanding of the multifaceted roles that disorder can play in complex materials. Arguably the most exciting and challenging regimes are the ones in which quantum fluctuations play a significant role. Disordered spin dimer compounds fall in to this general class of material, providing, at least in principle, well-controlled access to specific problems of interest, including Bose glass behavior, random singlet formation, and ordered states that arise as a consequence of quenched disorder. The proposed research will focus on the effects of disorder in this class of material, about which relatively little is known, and from which one can hope to glean important insights relevant to the broader class of quantum materials. Various chemical substitutions can be used to create different types and strengths of disorder in a variety of archetypal compounds, the effects of which will be studied via measurements of the low temperature thermodynamic properties as a function of the chemical composition. Single crystals of the materials studied will be grown in the PIs laboratory. The award will support the education and activities of a graduate student in these areas. ****Non-Technical Abstract****Disorder of one form or another is remarkably common in many advanced materials of technological importance, including high-temperature superconductors and materials exhibiting colossal magnetoresistance. Whether the disorder is an irrelevant distraction, that simply accompanies, for example, charge doping, or whether it plays a more central role in determining the associated phase diagrams of these materials is a matter of ongoing research and debate. Given the prevalence of disorder in these complex and incompletely understood materials, it is important to understand its effects in simpler and better controlled model systems. It is the purpose of this program to study disordered magnets in regimes which have not previously been extensively explored, with the broad aim of developing a deeper understanding of the effects of disorder in the broad class of quantum materials. The project involves both low temperature measurements, and also an extensive crystal growth effort. This crystal growth program has a broader impact by serving the larger condensed matter community via external collaborations, ensuring the wide availability of contemporary materials for the US condensed matter community, and addressing the perceived need for increased emphasis on materials synthesis within the US. The award will support the education of a graduate student in these technologically important areas.