Magnetic and electronic excitations in low-dimensional and nanostructured materials

对具有一个或多个亚微米范围长度的磁性材料的研究，如低维纳米结构和阵列，是由其巨大的技术潜力（用于高频器件，磁性存储器，快速开关等）驱动的。对于理论来说，需要在基本层面上理解这些长度尺度上的动力学过程。这为集体磁激发（或波）与电子激发的理论研究提供了主要动力。考虑到由于表面和界面的挑战性的影响是重要的，因为纳米结构的磁性材料可以显示在其本体组成材料中不存在的新特性。 我将研究磁性纳米元件阵列中磁自旋波的线性和非线性动力学，以及碳基纳米材料（如石墨烯）中相关的电子和磁性效应。例如，不断扩大的磁振子领域涉及人工介质，如图案化的薄膜，其磁性具有重复（或周期性）变化。可以使用这种周期性和施加的磁场来控制自旋波的频率和方向，作为器件应用的基础。在自旋电子学中，也有移动的电子电荷，在材料中产生电流;这些影响自旋波，允许进一步的设备应用。在非线性动力学中，自旋波之间的相互作用的影响开始发挥作用，我将在小尺度上研究这些影响。我将重点讨论的一些非线性效应包括自旋波衰减和不稳定性，特别是在强微波场中，以及磁玻色-爱因斯坦凝聚。磁性元件在其周期性或准周期性阵列中的选择为开发磁性器件应用的新特性提供了多种情况。 方法包括多体和量子场论（图解法，绿色函数，响应理论）。从以前的工作中，我有专门的自旋系统的方法，我将适应纳米材料在非线性制度与微波泵浦场正在应用的专业知识。我将利用与实验学家的合作，使用非弹性光散射，铁磁和电子自旋共振，微波光谱。我的研究将是重要的洞察力在非常小的长度尺度的动力学过程，并可能导致新的发展高频设备。当这些系统远离平衡时（由于微波场）或在更高温度下（当非线性过程增强时），了解它们的量子统计将是这项工作的重要方面。更好地了解石墨烯纳米结构中的磁效应是低维材料新应用的重要目标。

Research on magnetic materials with one or more lengths in the submicron range, as in low-dimensional nanostructures and arrays, is driven by their immense technological potential (for high-frequency devices, magnetic memories, fast switches, etc). For theory there is a need to understand at a fundamental level the dynamical processes on these length scales. This provides the primary motivation for this proposed theoretical research on the collective magnetic excitations (or waves) together with the electronic excitations. Taking into account the challenging effects due to surfaces and interfaces is important, since nanostructured magnetic materials may display novel characteristics that are absent in their bulk constituent materials. I will study the linear and nonlinear dynamics of magnetic spin waves in arrays of magnetic nano-elements and the related electronic and magnetic effects in carbon-based nanomaterials like graphene. For example, the expanding field of magnonics concerns artificial media like patterned thin films with a repeating (or periodic) variation in their magnetic properties. The frequencies and directions of the spin waves can be controlled using this periodicity and an applied magnetic field, as the basis for device applications. In spintronics there are also moving electronic charges, giving electric currents in the materials; these influence the spin waves allowing further device applications. In the nonlinear dynamics the effects of interactions between the spin waves come into play, and I will study these on the small length scales. Some nonlinear effects that I will focus on include spin-wave decay and instability, particularly in a strong microwave field, and the magnetic Bose-Einstein condensation. The choices of magnetic elements in their periodic or quasiperiodic arrays provide a variety of situations for exploiting new properties for magnetic device applications. Methods include many-body and quantum-field theories (diagrammatic methods, Green's functions, response theory). From previous work I have expertise in specialized methods for spin systems, which I will adapt for nanomaterials in nonlinear regimes with a microwave pumping field being applied. I will utilize collaborations with experimentalists using inelastic light scattering, ferromagnetic and electron-spin resonance, and microwave spectroscopy. My research will be significant for insights to dynamical processes at very small length scales and may lead to new developments for high-frequency devices. Understanding the quantum statistics in these systems when they are far from equilibrium (due to the microwave fields) or at higher temperatures (when nonlinear processes are enhanced) will be important aspects of this work. A better knowledge of the magnetic effects in graphene nanostructures is an important goal for new applications in low-dimensional materials.