Neutron Scattering Studies On Low Dimensional Quantum Magnets

Author : Wei He (Researcher in materials science)
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (13 download)

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Download or read book Scattering Studies of Magnetic and Charge Correlations in Two-dimensional Quantum Magnets written by Wei He (Researcher in materials science) and published by . This book was released on 2022 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of quantum magnets in two-dimensional systems is a forefront field in both materials science and condensed matter physics research. Such materials not only provide rich platforms for potential applications of novel materials but also further our understanding of basic physics. Neutron and x-ray scattering are powerful tools to explore the magnetic and charge correlations in these materials. This thesis describes the experimental investigation of two model systems in bulk crystalline form, one with a two-dimensional kagome lattice and one with a two-dimensional square lattice, both consisting of Cu2+ ions with spin-1/2. Strong quantum fluctuations give competing ground states or phases in both systems. Recently, barlowite Cu4(OH)6FBr has attracted much attention as the parent compound of a new kagome quantum spin liquid candidate. Our new synthesis method produced large single crystals of a new variant of barlowite, which has a higher symmetry space group compared to the previously reported one. Our elastic magnetic neutron scattering measurements reveal that the magnetic ground state of the new high-symmetry barlowite at low temperatures has a special pinwheel q = 0 magnetic order. In the intermediate temperatures, our numerical calculations and inelastic neutron scattering indicate that the kagome spins are in a potential pinwheel valence bond crystal state. Both of the two ground states are in close proximity to the long-sought quantum spin liquid state. The second part of my thesis is focused on the spin and charge correlations in high-Tc cuprate superconductors. Cuprate materials display intriguing physical phenomena due to the coexistence of various phases, which may interact with the superconductivity. The La-based family is a canonical example where both the spin and charge correlations could form "stripes". Magnetic neutron scattering reveals a rather surprising feature of the spin stripes in the model material La1.88Sr0.12CuO4: regardless of whether they are static or fluctuating, these stripes are always tilted from the high-symmetry direction of underlying lattices. Comparison with numerical simulations reveals the important role of the next-nearest neighbor electron hopping. Resonant soft x-ray scattering measurements offer important information about the charge order in another cuprate material stage-6 O-doped La2CuO4+y. By tuning both temperature and the dopant disorder level, we clearly observe two types of charge orders with distinct correlation lengths and behaviors at low temperatures. A coherent picture based on microscopic phase separation is proposed to explain the relationship between charge and spin orders with superconductivity in these materials.