Speaker: Prof. Xiangdong Zhu (University of California, Davis)

Time and Date: 13:30 pm, March 9, 2018

Place: Room 507 of Xingye Optical  Building, Handan Campus, Fudan University

Abstract:

Surfaces and interfaces of solid materials that consist of only a few atomic or molecular layers are a unique class of materials by themselves. Understanding properties of surfaces and interfaces is crucial from a number of standpoints. All forms of material synthesis and processing start at a solid surface, they are thus controlled by atomistic and molecular processes that occur at the surface. As physical dimensions of building blocks of solid-state devices continue to decrease down to a few nanometers, properties of the devices made of these nano-materials are significantly influenced by structural, electronic and transport properties of the surface that are distinct from those of the bulk. This is because the surface possesses different symmetries as required by its distinct physical setting. Furthermore, an interface separating two materials often hosts localized states with properties not found in either of the bulk materials such as classical surface plasmon polaritons in the vicinity of a metal surface, surface states on a topological insulator (driven by abrupt change in topological order parameter), and conducting states at the interface between polar and non-polar insulators (driven by polarization catastrophe).

   Measuring various properties of a solid surface by analyzing rich information in light reflection from the solid has many advantages such as non-invasiveness, in-situ detection (seeing it as it happens), access to deeply buried interfaces, being immune to volatile material synthesis and processing environments such as under high pressures and in liquid. Yet optical reflection from a solid surface contains an overwhelmingly large contribution from the bulk of the solid that needs to be suppressed. In this presentation, I show how one can characterize a solid surface or an interface with light reflection by taking advantage of various symmetry-breaking effects that dramatically reduces the contribution from the bulk. The symmetries include point-group symmetry, translational symmetry, time-reversal symmetry, and even s/p-polarization symmetry.

Biography:

Xiangdong Zhu (朱湘东) received a Bachelor of Science in physics from Peking University in 1982. He received a Ph. D. in Physics in 1989 from University of California at Berkeley. He joined the faculty in Physics Department of University of California at Davis afterward. He has been a full professor since 1998. He is a Fellow of American Physical Society and a Fellow of Optical Society of America. His research activities spread over various areas of linear and non-linear optical studies of solid surfaces and thin films.