(Georgia Institute of Technology, 2021-07-20)
Daum, Marcus J.
Quantum magnetism is a rich area of hard condensed matter physics where various energy scales and exchange parameters, coupled with lattice symmetries, lead to ground states of varying degrees of complexity. Through theoretical and experimental efforts, realizations of quantum many-body phenomena are found. This thesis presents recent work on several candidate materials which have been theoretically proposed to exhibit exotic states of matter as their ground state. These materials are carefully characterized using various theoretical and experimental means such as linear spin wave theory and inelastic neutron scattering to understand their ground states. In addition, work presented here displays effort to characterize, optimize, and design new neutron scattering instruments.
(Georgia Institute of Technology, 2020-03-16)
Ge, Luwei
Quantum magnetism is one of the most important branches in condensed matter physics because it serves as an excellent platform to realize model quantum many-body systems which are difficult to find elsewhere. Good understanding of the nature of magnetic excitations in such systems demands both experimental and theoretical efforts. This thesis presents comprehensive studies of the magnetic properties of several 3d transition-metal oxides for which the effective spin Hamiltonian forms quasi-1D, quasi-2D or 3D lattices. Primarily relying on advances in neutron scattering instrumentation and spin-wave theory, the work carefully examines the effectiveness of the theory of weakly interacting magnons in describing the elementary magnetic excitations of these insulators. By revealing the microscopic interactions of these systems and testing the applicability of spin-wave theory quantitatively, the work also hopes to offer useful insights or guidance to future investigations, which may extend to the entire field of quantum many-body physics.