Physics Colloquium: Topological phase transitions and Magnetoelectric effects in Heterostructures

Dr. Kang L. Wang, University of California, Los Angeles

Abstract: Topological quantum materials are a class of compounds featuring electronic band structures, which are topologically distinct from common metals and insulators. These materials have emerged as an exceptionally fertile ground for material science research and the studies have been expanded to Weyl semimetals and 2-D materials. One of most notable applications is spin orbit toque, giving rise to an energy efficiency magnetic memory. We will focus on recent material discoveries and experimental advancements of topological materials and their heterostructures. This talk will discuss the topological phase transitions of various topological heterostructures, beginning with quantum anomalous Hall in magnetic doped topological insulators as controlled by magnetic fields. Then the electric field is used to illustrate the phase diagrams, displaying quantum anomalous Hall and normal insulators. With the interface engineering of different magnetic layers or antiferromagnets, the axial electromagnetic or axion phase in a sandwiched structure is demonstrated. Various Chern insulator superlattices will also be discussed. We will also describe the spin orbit torque of topological films from ferrimagnetic materials and the use of chiral symmetry breaking for switching in topological insulator heterostructures. The perspective of topological spintronics will be discussed.

Biography: Dr. Kang L. Wang is currently a Distinguished Professor and the Raytheon Chair Professor in Physical Science and Electronics at the University of California, Los Angeles (UCLA). He is affiliated with the Departments of ECE, MSE, and Physics/Astronomy. He is also the Co-Director of UCLA Quantum Science and Engineering and the Director of the Joint Center of Green Nanotechnology – between UCLA and the King Abdulaziz City for Science and Technology, Saudi Arabia. He received his M.S. and Ph.D. degrees from the Massachusetts Institute of Technology and his B.S. degree from National Cheng Kung University (Taiwan). He was with HKUST as a Professor and the Dean of School of Engineering from 2000-2003. Previously, he also served as the Chair of UCLA Electrical and Computer Engineering from 1992-1996. His research areas include semiconductors, topological matters, spintronics/magnetics, nonvolatile electronics, and quantum information and computing as well as MBE.