Synthetic Design of Kitaev Magnets and Spin Liquids

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Nontechnical Abstract: Quantum spin liquids are magnetic materials which do not order even at temperatures approaching absolute zero. The theory of quantum spin liquids is very rich, with predictions of exotic new states of matter displaying unusual "fractionalized" excitations. Such fractionalized excitations behave as if they were new types of particles. This project seeks to find materials that show behavior characteristic of a particular kind of quantum spin liquid first proposed by the theorist Alexei Kitaev in the context of research on quantum computation. In this project new materials are designed in which Kitaev spin liquid physics is significant or even dominant. Careful characterization of the resultant properties is conducted, and the results will yield great insights into the nature of fractional excitations in a wide class of realizable materials, significantly advancing the state of forefront knowledge in modern condensed matter physics. This project also lays some necessary groundwork pointing the way to a possible solid-state technology for topologically protected quantum computing. This project also supports curriculum development of a new class, "Quantum Mechanics for Engineers", designed to help prepare engineering students for future careers in the development of quantum technologies. Technical Abstract: The research objectives of this project are to (1) design, discover, and characterize new materials in which Kitaev physics plays a crucial role in determining their magnetic properties; (2) study the spin excitations of the new materials with inelastic neutron scattering; (3) understand the data in the context of model Hamiltonians that go beyond the analytically soluble Kitaev model; and (4) use what has been learned to tune the materials and improve materials design principles, with the ultimate goal of finding a real material with a Kitaev quantum spin liquid ground state. Several design pathways to new Kitaev materials will be investigated: (1) intercalation of ruthenium trichloride into graphite; (2) use of ion-exchange reactions to replace Ir and Rh in honeycomb structures, and the investigation of these reactions in situ with powder neutron diffraction; (3) synthesis and crystal growth of osmium trichloride; and (4) synthesis of honeycomb and hyper-honeycomb hybrid inorganic-organic framework materials. The new materials are characterized with basic tools such as x-ray diffraction, magnetization, and specific heat. Attempts will be made to metallize some of the materials through chemical doping and in some cases ionic liquid gating. Promising materials will be studied with neutron diffraction and inelastic neutron scattering to gain an in-depth understanding of the magnetic ground state and quasiparticle excitations. The knowledge gained from characterization will be used to help design the next generation of materials. Undergraduate students involved in this project will be trained in materials synthesis; graduate students will be trained in both materials synthesis and neutron scattering.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.