CAREER: Anomalous spin dynamics in triangular quantum magnets: from materials discovery to quantitative neutron spectroscopy

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Non-Technical: Magnetic phenomena are essential to the quantum materials revolution. Complex interactions between spins - quantized "compass needles" carried by electrons bound to crystal lattices - provide magnetic matter with desirable quantum coherence properties. For instance, a special state of matter called a "quantum spin-liquids" could be used for new quantum information and sensing technologies. However, these strange new quantum states involve many spins and are incredibly challenging to both predict and measure in real materials. This experimental research brings together materials science, spectroscopy, and modeling to discover if and how macroscopic quantum effects emerge in networks of interacting spins. The project focuses on an unexplored set of inorganic compounds that are designed for new types of behavior. This research will utilize neutron spectroscopy to accurately map spin states in custom-grown samples and so, probe directly predictions from realistic theoretical models. Professional researchers in the project will team with high-school students, their teachers, and undergraduate students to generate a long-lasting interest for materials research and provide the network needed to support the future quantum workforce. Participants not only train in sample growth and cryogenic measurements in the principal investigator's laboratory, but also get involved in experiments at world-class facilities for crystal growth and neutron scattering, for instance at Oak Ridge National Laboratory. Participants subsequently engage the general and university public to expose the beauty of "the Universe" within condensed matter and communicate the promise of the quantum materials revolution.Technical Abstract: Correlated magnetic insulators are unique materials at the heart of the current quantum revolution. They often provide definitive answers to a universal question: how do macroscopic quantum phenomena emerge in crystalline matter from assemblies of atomic-scale entities? Several systems of interacting spins host desirable quantum phases with no classical analogues - characterized by a high degree of entanglement, their excitations are non-local like spinons or Majorana fermions. In most cases, however, these many-body states are difficult to predict with existing techniques. Realizing and detecting genuine quantum phases in real materials is therefore extremely challenging. This experimental research merges in-house efforts with the use of world-class centers for crystal growth and inelastic neutron-scattering in the United States to track and expose quantum phenomena in triangular networks of interacting spins. Low-dimensional and geometrically frustrated, triangular-lattice antiferromagnets are at the boundary between semi-classical and quantum behaviors. This tendency, when combined with spin-space anisotropies and quantum fluctuations tuned by compositional variations, produces novel phases and quasiparticles. The research activities advance inelastic neutron scattering instrumentation and data analysis tools to accurately map spin excitations in laboratory-grown samples and to benchmark predictions from realistic models. Three related directions are explored: (1) nonlinear dynamics and possible breakdown of magnon quasiparticles in transition-metal compounds; (2) spin-orbit-induced anisotropies and spin-liquid phenomenology in rare-earth magnets; (3) discovery and characterization of new triangular-lattice materials. Teams of high-school, undergraduate and graduate students participate in every step of the research process in the principal investigator's laboratory and at large-scale central facilities. Mentoring of participants by professional researchers provides the scaffolding needed to support the future quantum workforce.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.