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

本研究的主要目的是对波动扰动（称为集体激发）进行理论研究，这种扰动可能发生在低维固体结构中，通常在一个或多个维度上的长度尺度可能小到几个（或几十个）纳米。例如，扰动可以是磁化（如自旋波或磁振子）、原子振动（如声子）或电磁场（如极化激元）中的波动。 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制造到非常精确的程度。 一个共同的特点是，波或激励被广泛修改，由于非常小的长度尺度和边界区域（表面和界面）在这样的结构，因此可能会显示出与那些在散装材料的性质完全不同。 对这些效应的基本理解是重要的，无论是对于基础物理学还是对于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）。 我对这些结构和材料的非线性动力学特性的新方面感兴趣，即，在波相互作用的情况下。 这是除了需要扩展以前的工作在线性（或非相互作用）制度，以不同的材料和几何形状（如纳米管和纳米点阵列，或图案化的表面）。 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（如量子和经典的蒙特-卡罗方法）。 详细的应用程序将作出非弹性光散射和其他实验技术调查在这些系统中的激发。 该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，由于空间局部化和相互作用的竞争类型，可能会发生有趣的效应。

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.