NMR studies of quantum matter under stressed conditions

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Non-technical abstractAdvancing the general understanding of quantum materials is of fundamental interest and importance, as it gives the ability to optimize materials properties for practical use. Since progress often turns on manipulation and control of properties, central to the project is the development and use of devices capable of imposing anisotropic pressure to achieve those ends. The primary measurement tool is nuclear magnetic resonance (NMR), applied in combination with the uniaxial pressure, in variable magnetic fields and to very low temperatures (1 K). Sought after is evidence for stabilization of otherwise inaccessible states of matter, and clarification of research questions unresolved by other means. Our objectives include the application of the uniaxial pressure method to layered materials where means have been quite limited until now. NMR is used because it is a local probe of the electronic environment, sensitive to both charge and spin degrees of freedom. Graduate and undergraduate students are trained and gain expertise in cryogenic, radiofrequency, and simulation technologies, with opportunities to collaborate with research groups in the United States and abroad, such as the National MagLab in Tallahassee. By way of the associated collaborations, the students benefit from interactions with scientists of complementary expertise, through remote conferencing or on-site visits.Technical abstractThe project objectives include the further development of, and broadening the use of the stress/strain method while exploiting the capabilities of magnetic resonance. The purpose is for observation, control, and understanding of phenomena and phases in selected quantum materials. NMR is well-suited for this task because it is a probe of the local charge and magnetic environment, and its implementation is compatible with the other experimental constraints. Tuning quantum matter by strain has potential for broad application, since it can be varied continuously, in situ. Specifically targeted in this project are materials exhibiting nearly degenerate topological superconducting phases, unsolved problems in unconventional superconductivity, and frustrated quantum magnets. The tunability is of a different origin in the three model systems. In one, the proximity of the Fermi energy to a van Hove singularity is key. In a second, the relative stability of nearly degenerate ground states is important. In a third, the strength of frustrated interactions are manipulated. Building on the demonstrated success in exploring the physics of the normal and superconducting states of an archetypal Fermi Liquid, further constraints on the superconducting state remains a top priority. In addition, the method is extended to study in some detail the strain-induced breakdown of the Fermi Liquid state and its influence over physical parameters and collective fluctuations. The suitability of the method to Van der Waals materials are advanced in layered chalcogenide systems, including a charge density wave material, and a topological superconductor considered to support nearly degenerate ground states. The frustrated interactions in a two-dimensional quantum magnet are tuned using the strain device.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.