Exotic Magnetic Ground States and Ground State Selection in Quantum Materials

点击翻译按钮获取中文摘要

The ground states of most magnetic materials, and all magnetic materials which are well understood, are characterized by long range order and conventional elementary excitations, such as spin waves. We are specifically interested in families of new magnetic materials, where this isn't the case; that is where a disordered low temperature phase can persist due to the presence of very strong spin fluctuations. This is a very topical area of contemporary condensed matter research as it is widely believed that if a conventional ordered state can be suppressed at low temperatures, it opens a window for an exotic ground state to be manifest.  Appropriate quantum disordered states are thought to possess qualitatively new and remarkable physical properties, such as delocalized quantum spin excitations, that may provide a platform for quantum computation. Strong spin fluctuations can be encouraged in three ways in magnetic materials: magnetic moments can decorate local geometries (typically based on triangles and tetrahedra) in solids which are incompatible with a simple ordered state - this is referred to as geometrical frustration; S=1/2 and effective S=1/2 magnetic moments, which support extreme quantum fluctuations, can be made to decorate the lattice; and finally the magnetic lattice can be effectively two or one dimensional due to a three dimensional crystal structure which is made of a stacking of magnetic planes, or a bunching together of magnetic chains.  This proposal seeks to explore new magnetic materials which do precisely this. By carrying out advanced characterization, primarily with new neutron and x-ray scattering techniques we aim to elucidate the nature of the exotic ground states which ensue in such materials, such that the principles that underlie the novel phenomena they display can be fully understood. This proposal seeks to carry out programs of neutron scattering measurements on several families of exotic magnetic materials that we will grow in single crystalline, polycrystalline and epitaxial thin film form. We are in the midst of a renaissance in the capabilities available to carry out forefront inelastic neutron scattering.  The net result is that new neutron scattering instrumentation provides qualitatively different, and much more comprehensive, information on materials than was possible six years ago. This proposal seeks to apply this new infrastructure to several topical problems related to exotic magnetic ground states in new materials. A crucial component and starting point for the themes of this proposal is a program of sophisticated materials preparation and crystal growth which will provide new magnetic materials in appropriate forms. We are exceptionally well positioned, both with respect to our capacity to produce materials of interest, and with respect to access and expertise associated with the new neutron scattering infrastructure, to make real progress in this very topical area of condensed matter physics.