High Pressure NMR Studies of Doping and Inhomogeneity in Strongly Correlated Electron Systems

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Nontechnical abstract:The objective of this project is to develop a fundamental understanding of the microscopic response of strongly correlated electron systems to doping and pressure. By their very nature, these materials are highly sensitive to impurities, and dopants are frequently used to tune their properties. However, little is known about the microscopic behavior in the vicinity of dopant atoms, and how the impurities collectively modify bulk properties. This research project employs Nuclear Magnetic Resonance to probe high quality single crystals using a state-of-the-art diamond anvil pressure cell. A key focus of this project is graduate education, and it incorporates educational outreach activities to a broad range of students. Outreach efforts to a local elementary school include science projects that actively engage children in the scientific method and a course on condensed matter science for adult and senior citizen students through the university extension office. Technical abstract:Strongly correlated electron materials hold tremendous potential for new technologies, but a fundamental understanding of their relevant many-body physics remains one of the greatest challenges in condensed matter physics. Chemical doping is widely used as a straightforward mechanism to tune the ground state of these materials, often revealing rich phase diagrams including unconventional superconductivity and non-Fermi liquid behavior. At the microscopic level, however, dopants strongly perturb the electronic degrees of freedom, in some cases giving rise to non-universal behaviors such as phase segregation and inhomogeneous glassy dynamics. These strongly inhomogeneous responses can mask intrinsic phenomena, and complicate the interpretation of bulk measurements. This project addresses the differences between doping and pressure as tuning parameters through Nuclear Magnetic Resonance studies of two prototypical correlated electron systems: the iron pnictide and heavy fermion superconductors. The research team is developing advanced new equipment to explore the microscopic behavior using diamond anvil cells to achieve large hydrostastic pressures, and mechanical clamps to achieve uniaxial strain in single crystals. Both techniques enable the study of the microscopic response of materials under conditions that have never been investigated with magnetic resonance previously. The outcome of this research is a more complete understanding how strong correlations in the presence of disorder influence macroscopic properties.