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

这项研究的主要目标是对低维固体结构中可能发生的波状扰动进行理论研究，这种扰动称为集体激发，其中一个或多个维度的长度尺度通常小至几个(或几十个)纳米。例如，扰动可以是磁化强度(如自旋波或磁振子)、原子振动(如声子)或电磁场(如极化子)的波动。感兴趣的结构类型包括薄膜、多层(例如具有规则重复图案或周期性的超晶格)、纳米线、纳米管和纳米点(单独或以阵列形成)。所有这些都能够通过现代生长技术以惊人的精度制造出来。一个共同的特征是，由于这种结构中很小的长度尺度和边界区域(表面和界面)，波或激励被广泛修改，因此可能表现出与块体材料完全不同的性质。对这些效应的基本了解对于基础物理学和确定它们的应用潜力(例如，作为高频纳米结构设备和信息存储设备)都是重要的。我感兴趣的是与这些结构和材料的非线性动力学特性有关的新方面，即波相互作用的情况。此外，还需要将以前在线性(或非相互作用)区域中的工作扩展到不同的材料和几何形状(例如，纳米管和纳米点阵列，或图案化表面)。理论方法包括使用先进的分析技术(如多体理论和量子场论)，在某些情况下，还包括数值模拟(如量子和经典蒙特卡罗方法)。文中将详细应用非弹性光散射和其他实验技术来研究这些系统中的激发。这个项目的主要重点将是有序磁性材料中的线性和非线性自旋波，由于空间局部化和竞争类型的相互作用，可能会出现有趣的效应。

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.