Ultrafast study of spin-orbit materials by time and spin resolved photoemission spectroscopy

非技术文摘：电子自旋是材料的一种令人着迷的特性。它的二元性质“向上或向下自旋”是量子化的最简单例子，因此，它经常被用作量子力学教科书的起点。电子自旋的磁矩是丰富磁场的主要驱动力，它与轨道运动的相互作用（称为自旋轨道相互作用）可以产生显著的后果，如铁磁体中的异常霍尔效应。虽然在某种程度上存在于所有材料中，但直到最近才发现了一类被称为拓扑绝缘体的新材料（在体上绝缘但表面是金属的材料），人们已经意识到自旋轨道耦合也可以成为非磁性材料中美丽新现象的驱动因素。本项目主要研究与基础材料科学研究和技术相关的一系列材料中自旋轨道耦合的新兴自旋依赖物理，主要集中在三维拓扑绝缘体上。参与该项目的学生将在材料表征方法和不断发展的光电子能谱技术方面发展专业知识，成为新兴的实验自旋动力学领域的未来领导者。这将为他们在工业、学术界或政府实验室的科学事业做好准备。与加州大学伯克利分校的外展项目相结合，该项目将涉及少数民族和年轻学生，以灌输对科学的热情和好奇心。技术摘要：当前凝聚态物理学的一个突出课题是开发利用自旋自由度的材料和器件，而传统电子学仅使用电子电荷。自旋轨道耦合材料领域的迅速发展和最近拓扑绝缘体的发现为这种控制提供了一条令人兴奋的途径。拓扑绝缘体是一种具有体带隙和无质量狄拉克费米子表面态的绝缘材料，其自旋非简并并具有独特的自旋动量锁定，其中状态沿着由其晶体动量方向决定的空间方向强烈自旋极化。该项目旨在促进我们对三维拓扑绝缘体中的自旋轨道物理的理解，以及拓扑保护表面态与对称破缺材料之间的相互作用，并寻找用光操纵由此产生的自旋纹理的新方法。这是利用时间、自旋和角度分辨光谱学的新技术实现的。参与本项目的学生将在真空、材料表征、激光、光学和光电子能谱等领域发展专业知识。该项目还将通过学年指导和暑期研究项目，针对少数族裔和年轻学生。

Non-technical abstract: The electron spin is a fascinating property of materials. Its binary nature "spin-up or -down" acts as the simplest example of quantization, and as such, it is often used as the starting point for quantum mechanics textbooks. The magnetic moment of the electron spin is a primary driver of the rich field of magnetism, and its interaction with the orbital motion (known as spin-orbit interaction), can have significant consequences such as the anomalous Hall effect in ferromagnets. Although present in some degree in all materials, only recently with the discovery of a new class of materials known as topological insulators (materials insulating on the bulk but metallic on the surface), it has been realized that spin-orbit coupling can be the driver of beautiful new phenomena in non-magnetic materials as well. This project focuses on an experimental investigation of the emergent spin dependent physics from spin-orbit coupling in a range of materials relevant to both fundamental materials science research and technology, with main focus on the three dimensional topological insulators. Students working on this project will develop expertise in material characterization methodologies and the evolving techniques of photoelectron spectroscopy to become future leaders of the new growing community of experimental spin-dynamics. This will prepare them for scientific careers in industry, academia or government laboratories. In conjunction with outreach programs at UC Berkeley, this project will involve minorities and young students to instill passion and curiosity for science.Technical abstract: A prominent topic in current condensed matter physics is the development of materials and devices that utilize the spin degree of freedom, in contrast to traditional electronics, which use only the electronic charge. The rapidly expanding field of spin-orbit coupled materials and the recent discovery of topological insulators constitute one exciting route to such control. Topological insulators are insulating materials characterized by a bulk bandgap, and massless Dirac fermion surface states which are spin non-degenerate and features unique spin-momentum locking in which states are strongly spin polarized along a spatial direction determined by the direction of their crystal momentum. This project seeks to advance our understanding of spin-orbit physics in three-dimensional topological insulators and on the interaction between topologically protected surface states and symmetry breaking materials, as well as to search for new way to manipulate the resulting spin texture with light. This is achieved by use of novel technique of time-, spin- and angle resolved photoemission spectroscopy. Students working on this project will develop expertise in the field of vacuum, material characterization, laser, optics and photoelectron spectroscopy. The project will also target minorities and young students through school-year mentorship and summer research projects.