NMR Studies of Nematicity in Strongly Correlated Electron Systems under Uniaxial Strain

University Of California-Davis, Davis CA

Investigators

Abstract

Nontechnical Abstract: In high temperature superconductors an electronic state with zero resistance emerges at low temperatures. Superconductivity is a quantum mechanical phenomenon that has a wide range of potential applications, including magnetic levitation and energy transport without dissipation, capable of changing the society and economy in a transformative way. But superconductivity is still poorly understood and is seen in various types of materials. A particularly interesting case occurs for nematic materials, in which the electronic behavior spontaneously becomes anisotropic. This behavior can be induced in the laboratory by applying strain to the crystal, which may alter its physical properties. We aim to investigate the microscopic behavior using magnetic resonance to study the electronic response to strain. This project will support the education of undergraduate and graduate students, as well as a broad audience of senior citizens via a new course on quantum mechanics without equations for the public through the university extension office. Technical Abstract: The objective of this project is to develop a fundamental understanding of quantum critical nematic fluctuations in strongly correlated electron materials. Electronic nematic order has been observed in the iron and cuprate superconductors, and evidence suggests that nematic fluctuations may be responsible for the superconducting pairing mechanism and the non-Fermi liquid behavior at optimal doping in these materials. However, the presence of multiple types of order parameters and their fluctuations complicate the interpretation of experiments and preclude the identification of the essential physics behind these phenomena. Recent evidence suggests that electronic nematic fluctuations may be responsible for superconductivity in some cases. However, multiple types of electronic order parameters can be present simultaneously, and by their very nature strongly correlated systems are highly sensitive to impurities, giving rise to microscopic inhomogeneity that obfuscates experimental observations. As a result, there is no clear picture as to what extent electron nematicity is central to the fundamental physics of high temperature superconductivity in the iron and cuprates materials, or whether it is simply a curious epiphenomenon. This project will answer this question through nuclear magnetic resonance studies of cuprates, vanadates, iridates and iron pnictide materials under uniaxial strain in regimes of phase space that have never been investigated. These investigations will disentangle the roles of disorder, nematicity, and antiferromagnetism at play in the normal state of the high temperature iron and cuprate superconductors, and will also explore new regimes of phase space using uniaxial strain as a thermodynamic tuning variable. The outcome of this project will be a more complete understanding of the role of quantum critical nematic fluctuations and the essential physics of strongly correlated electron materials. 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.