Theory of magnetic and nonmagnetic excitations in low-dimensional and nanostuctured materials

点击翻译按钮获取中文摘要

The primary objective of this research is a theoretical study of the wave-like disturbances, known as collective excitations, that can occur in low-dimensional solid structures where typically the length scale in one or more of the dimensions may be as small as a few (or a few tens of) nanometres. The disturbances can, for example, be fluctuations in the magnetization (as in a spin wave or magnon), in atomic vibrations (as in phonons), or in electromagnetic fields (as in polaritons). The types of structures of interest include thin films, multilayers (such as superlattices which have a regular repeat pattern or periodicity), nanowires, nanotubes and nanodots (either singly or formed in arrays). All of these are capable of being fabricated to remarkable precision by modern growth techniques. A common feature is that the waves or excitations are extensively modified due to the very small length scale and the boundary regions (the surfaces and interfaces) in such structures, and therefore may show properties quite different from those in bulk materials. A fundamental understanding of these effects is important, both for the basic physics and for identifying their potential for applications (e.g, as high-frequency nanostructure devices and information storage devices). I am interested in novel aspects concerned with the nonlinear dynamical properties of these structures and materials, i.e., in cases where the waves interact with one another. This is in addition to the need for extending previous work in the linear (or noninteracting) regime to different materials and geometries (e.g. arrays of nanotubes and nanodots, or patterned surfaces). The theoretical methods include the use of advanced analytical techniques (such as many-body theory and quantum field theory) and, in some cases, numerical simulations (such as quantum and classical Monte-Carlo methods). Detailed applications will be made to inelastic light scattering and other experimental techniques for investigating the excitations in these systems. A major emphasis in this project will be to linear and nonlinear spin waves in ordered magnetic materials, where interesting effects can occur because of spatial localization and competing types of interactions.