Non-Technical Abstract: The technological drive to find new materials with controllable desired properties for advance applications in information, sensing, and energy technologies, requires understanding of the new forms of quantum matter. A central issue in quantum materials research is study of the combined effects of strong electronic interactions with local entanglement of spin (the magnetic moment of electron) and orbital degrees of freedom, so-called spin-orbit coupling. Predicting emergent properties represents a huge theoretical problem since the presence of the spin orbit entanglement implies that the spin is affected by its orbiting an atomic nucleus, and therefore the spin of an electron is not well defined. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local charge/orbital or local spin properties. This award supports research on extensive study of these emergent phases using local microscopic measurements, designed to concurrently probe spin, charge/orbital, and lattice properties. The transformative goal of this research is to identify an appropriate theoretical framework for describing systems with both strong correlations and SOC and so promote the discovery of materials with designed properties. The researchers at Brown University and National High Magnetic Field Laboratory simultaneously probe magnetic and orbital/charge properties while subjecting the samples to applied magnetic field and varying the amount of electronic charge, to tune competing interactions. A strong educational component is imbedded in the project by establishing a challenging training ground for students, both graduate and undergraduate, who will be involved in the scientific, modeling, and technical developments. The work at the National High Magnetic Field Laboratory and other international user facilities will be of particular benefit in training students.
This research program focuses on the experimental investigation of emergent orders in strongly correlated electron systems with varying amount of spin-orbit coupling (SOC) using nuclear magnetic resonance (NMR) techniques with the goal to decipher the complex interplay between different interactions that leads to the emergent quantum states of matter. These NMR measurements are designed to concurrently probe spin, charge/orbital, and lattice degrees of freedom (DOF) at the relevant low energy scales for an extensive study of these emergent phases. Initial emphasis is on double-perovskites materials, investigated by NMR on nuclei with finite quadrupolar moment. The microscopic nature of orbital and magnetic states is inferred by correlating these findings with the dynamical effects associated with low energy quasiparticles. Furthermore, the comparison of experimental data to theoretical models (and simulations) is carried out, in order to build a comprehensive understanding of the ways in which the spin, lattice, charge, and orbital DOF cooperate, compete, and/or reconstruct in complex materials to produce novel phenomena and/or magnetic states. Specific to the stated goals, the competing interactions are tuned by external parameters, such as magnetic field, and coordinated variations in chemical pressure, charge doping, and strength of SOC. To achieve these objectives, the research team is developing a novel NMR approach based on the use of NMR concepts from quantum information science (QIS) to untangle spin and orbital degrees of freedom, and measure separate linear response in the spin and charge channels. The study is extended to topological Kondo insulators to provide a general understanding of intrinsic properties arising from the interplay of strong correlations, SOC, multi-orbital, and multi-valence DOF. The transformative goal of the research project is to help identify an appropriate theoretical framework for describing systems in which correlations and SOC are of comparable energy scale and neither can be treated perturbatively.
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.
