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

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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.