University of California, Riverside

报告摘要（Abstract）:
Two dimensional (2D) systems, such as atomically thin materials and material interfaces, offer a rich ground to discover new types of electronic states. Recent development of our understanding on topological orders has led to a series of important discoveries in 2D systems, in particular, the quantum Hall, quantum spin Hall, and quantum anomalous Hall effects. In these systems, the topological order manifests itself as distinct properties in the bulk and edges. Typically, the bulk resides in an energy gap with a non-trivial topological number, while gapless excitation remains near edges, leading to quantized transport. Conventional transport technique has been a powerful tool to study the behavior of edge conduction. On the other hand, techniques capable of probing the bulk state have been challenging. In this talk, I will present studies on 2D topological systems using Microwave Impedance Microscopy (MIM), a scanning probe technique that senses materials’ capacitance and conductivity on the nanoscale. Specific examples include: the quantum Hall effect in graphene where we observe an unexpected correlation between transport and bulk Landau level filling; the quantum spin Hall effect in HgTe quantum wells and monolayer WTe2 where we examine the nature of the edge states under broken time-reversal symmetry; lastly the quantum anomalous Hall effect in magnetic TI thin films where we map out the spatial conductivity profiles under quantization conditions. In all these systems, the combination of transport and MIM measurements provide a more comprehensive understanding than the simplified picture often assumed in the transport analysis.

报告人简介：
Dr. Yongtao Cui is an Assistant Professor in the Department of Physics and Astronomy at the University of California, Riverside. He obtained his B.Sc. from Peking University in 2005, and his PhD degree in Applied Physics from Cornell University in 2011. His PhD study focused on the characterization of magnetic dynamics of a nanomagnet excited by spin transfer torque. He then moved to Stanford University for postdoc research on the development of Microwave Impedance Microscopy and applying it to the study of nanoscale electronic states in quantum materials. He joined UC Riverside in the summer of 2016.

联系人：翁红明（82649941）