Nuclear Magnetic Resonance Study of Emergent Orders

Brown University, Providence RI

Investigators

Abstract

Non-Technical Abstract: The technological drive to find new materials with controllable desired properties for advanced 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 correlations with local entanglement of spin and orbital degrees of freedom, so-called spin-orbit coupling (SOC). Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. 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 uniaxial stress, strain, and applied magnetic field, 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. Technical Abstract: This research program focuses on the experimental investigation of emergent orders in strongly correlated electron systems with notable 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 at the relevant low energy, while subjecting the samples to symmetry-breaking uniaxial stress, strain, and magnetic field. To achieve these objectives, the researchers develop a novel NMR approach, based on the use of surface coils, to allow for both in-situ stress and strain variation. Initial emphasis of the research is on Fe-based superconductor model systems. The team performs NMR in the same experimental conditions of applied uniaxial stress and strain as those of transport properties. Correlating these findings provides a picture of the microscopic nature of electronic liquid crystals (nematic) and magnetic states; the coexistence of the multiple order parameters, and of the role their associated fluctuations play in establishing unconventional superconductivity. To provide general understanding of intrinsic properties of electronic nematic phases, this work extends from unconventional superconductors (doped Mott insulators) to the magnetic Mott insulators with strong SOC (e.g. 5d-electrons double perovskite systems). The transformative goal of the research is to understand electronic mechanism of nematicity in systems with both localized and itinerant electrons, and 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. The participating graduate and undergraduate students will gain valuable research experience at the National High Magnetic Field Laboratory.