讲座题目：Nonlinear Optical Studies of Condensed Phases: From Equilibrium Structure to Non-Equilibrium Dynamics

主讲人：John A. McGuire

主持人: 程亚教授

讲座时间：2017.5.12上午10：00

讲座地点：理科大楼A814室

报告人简介：

John A. McGuire

Assistant Professor of Physics, Michigan State University, U.S.A. 2009.08 - present

National Science Foundation CAREER award 2013

Ph.D., University of California, Berkeley 2004.12

advisor: Professor Yuen-Ron Shen （沈元壤）

Postdoctoral Fellow, University of California, Berkeley 2005

Postdoctoral Research Associate, Los Alamos National Laboratory, U.S.A. 2006.02-2009.08

Supervisor: Dr. Victor Klimov

Research fields: time-resolved and nonlinear optical studies of low-dimensional systems (layered materials and quantum dots) and interfaces.

报告摘要：

The central questions in condensed matter physics concern the electronic structure and symmetries of systems at equilibrium, fluctuations of equilibrium systems, and relaxation of non-equilibrium states. I will describe our investigations of these questions in low-dimensional and interfacial systems via ultrafast and nonlinear optical techniques. Examples will include the change of equilibrium electronic structure in atomically thin layered GaSe[1] and the electronic structure of short-lived biexcitons in graphene quantum dots[2]. More attention will be given to the dynamics of the hydrogen-bond network of water at an interface with a hydrophobic surface[3,4]. What makes water special is its strong hydrogen-bond network, which is highly dynamic under equilibrium conditions at room temperature. However, this network is terminated at an interface, which leads to different properties of the interface compared to the bulk. We can probe these differences by using sum-frequency generation as a surface-sensitive probe after infrared excitation of the OH stretch modes of interfacial water. In particular, at a hydrophobic surface, we probe the dangling OH groups, i.e., those OH groups that point toward the hydrophobic surface and so do not form hydrogen bonds. The evolution of the excited population of the dangling mode is dominated by reorientation to a hydrogen-bonded configuration, which we monitor by time- and polarization-resolved sum-frequency generation. I will conclude with a discussion of our prospective application of nonlinear optical approaches to studying exciton interactions in layered systems and novel orders in correlated and topological systems.

[1] Y.H. Tang, et al., Phys. Rev. B94, 125302 (2016).

[2] C. Sun et al., Nano Lett.15, 5472 (2015).

[3] C. Sun et al., Phys. Rev. Lett.113, 107401 (2014).

[4] S.H. Xiao et al. J. Amer. Chem. Soc.138, 5551 (2016).