Dynamics of Condensed Matter Systems

我的研究集中在微观结构的时间演化上。由于微观结构取决于样品的历史，因此需要非平衡热力学才能理解它。材料的微观结构是其大部分物理和机械性能的核心。不仅故障率，而且许多其他重要的性能，包括抗拉强度、化学反应性和磁矫顽力，都关键取决于这种形态。这些结构的典型长度尺度为微米。许多先进材料，通常被称为“现代太空时代”材料，通过精细和复杂的加工技术控制其微观结构，从而获得其性能。理解微结构是如何产生的，如何刻画它们，它们如何在时间上演化，以及理想地控制它们，这是物理学中的一个重要的基本问题。无序系统中相干性和关联性的性质和作用仍未被完全理解。实时原位衍射测量，使用时间分辨衍射或X射线光子相关光谱，允许在类似于传统工艺的条件下测量微结构，因此非常适合于这些研究。开发的两个主要领域是更好的原位时间分辨散射的仪器和技术，以帮助解决这些问题，并利用它们更好地理解上述物理学。我的观点是，物理学最大的影响之一是发展了其他科学所使用的仪器。为了追求这一目标，我参与了SLAC使用最亮的x射线同步加速器源和新的x射线激光器的仪器的设计和建造。最新的项目是一个新的时间分辨飞秒电子衍射装置。这是与B.Siwick和D.Cooke合作进行的，他们都是McGill的教员。这种强调使我们能够在系统脱离平衡以及接近新的平衡或亚稳态时测量材料。除了继续我目前的研究，还有一个新的项目是与Siwick教授合作进行超快电子衍射(UED)。第一组材料是电荷密度波系统(NbSe_2、TiSe_2、TaSe_2和TaS_2)，其中光激发与电子和声子动力学耦合。为了研究这些影响，需要能够以亚皮秒的时间尺度测量结构

My research concentrates on the time evolution of microstructures. Since the microstructure depends on the history of the sample it requires nonequilibrium thermodynamics for its understanding. The microstructure of a material is central to most of its physical and mechanical properties. Not only failure rates, but many other important properties including tensile strength, chemical reactivity and magnetic coercivity, depend crucially on this morphology. The typical length scales of these structures is micrometers. Many of the advanced materials, often denoted as ``modern space age'' materials, obtain their properties from controlling their microstructure by careful and sophisticated processing techniques. It is an important fundamental problem in physics to understand how microstructures arise, how to characterize them, how they evolve in time and ideally to control them. The nature and role of coherence and correlations in disordered systems is still not fully understood. Real-time in-situ diffraction measurements, using either time resolved diffraction or x-ray photon correlation spectroscopy, allow measurements of the microstructure under conditions similar to conventional processing and therefore are ideally suited for these studies. Two main areas of development are better instrumentation and techniques for in-situ time-resolved scattering to help address these issues and to better understand the physics described above using them. It is my opinion is that one of the largest impacts of physics has been to develop the instrumentation used by the rest of science. In order to pursue this objective, I am involved in designing and building instrumentation to use the brightest x-ray synchrotron sources and the new x-ray laser at SLAC. The newest project is a new time-resolved femtosecond electron diffraction setup. This is in collaboration with B. Siwick and D. Cooke, both faculty at McGill. This emphasis has allowed us to measure materials while the system is being taken out of equilibrium and as it approaches the new equilibrium or metastable state. Besides continuing my current research, a new project is a collaboration with the Prof. Siwick to perform ultrafast electron diffraction (UED). A first set of materials are charge density wave systems (NbSe2, TiSe2, TaSe2 and TaS2) where optical excitations couple to the electron and phonon dynamics. The ability to measure the structures with sub-picosecond time scales is needed o study these effects