Quantum Spin Liquids in Correlated f-Electron Compounds

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Nontechnical Abstract: Almost all materials will ultimately settle into an ordered state at the lowest temperatures. The situation would be much different in a universe that is one- or two dimensional, and where the exotic quantum spin liquid state may emerge. Understanding the ways in which the transport of heat and charge occurs in such a state is just beginning, and controlling it to create practical devices and sensors has emerged as a central challenge. This project will identify and synthesize new materials in search for a metallic quantum spin liquid. Neutron scattering experiments will be carried out at national facilities at Oak Ridge National Laboratory and at the National Institute of Standards and Technology. Both undergraduate and graduate students participate in all aspects of these experiments, receiving thorough training and broad experience in measurement techniques and applications that will prepare them to become effective future users of these national facilities. Technical Abstract: Quantum Spin Liquids (QSL) occur when magnetic order is overwhelmed by strong quantum fluctuations, giving rise to massively entangled ground states with unusual excitations, often with topological character. While metallic QSLs are expected to have a much richer range of phase behaviors, the few QSL systems discovered so far are all insulating. The discovery of intrinsically metallic QSLs where frustrated moments are coupled to itinerant conduction electrons has the potential to realize and to test theoretical predictions of exotic states and phases like unconventional superconductivity, ferromagnetism, and Dirac metals where excitations have photon-like dispersions. This project seeks to find the first examples of metallic QSLs among the f-electron based heavy fermions, and to explicate how the breakdown of conventional magnetic order or alternatively the formation of magnetic moments via the collapse of the Fermi surface can be generic routes to QSL formation in metals. The experimental program is based on the metallic R2T2X (R=Ce,Yb) compounds, where strong quantum fluctuations arise from competition between dimerization and magnetic order in both planar and chainlike morphologies. The high quality single crystals required to support this experimental program will be grown in our lab from metallic fluxes. Neutron diffraction, magnetometry, heat capacity, and electrical transport measurements will be primary tools for explicating the underlying magnetic and electronic phase diagrams, supplemented by inelastic neutron scattering measurements that will assess the corresponding development of magnetic fluctuations and correlations.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.