| 报告题目 | Colloidal suspension as a model system of condensed matter: investigating crystal nucleation and glass vibrational modes |
| 报告人 | 谭鹏 博士 |
| 报告人单位 | 香港中文大学物理系 |
| 报告时间 | 2014-03-04 |
| 报告地点 | 合肥微尺度物质科学国家实验室九楼会议室 |
| 主办单位 | 合肥微尺度物质科学国家实验室、物理学院 |
| 报告介绍 | 报告摘要：
Because atoms and molecules are small in size and fast in motion, it is difficult to visualize them directly and probe their microscopic motions, which precludes a microscopic understanding on dynamics of condensed matter, such as phase transition kinetics and collective vibrations (normal modes). In contrast, micrometer-sized colloidal particles can serve as good model systems for these studies because thermal motions can be directly visualized and measured with video microscopy.
We will introduce our two recent experimental studies in colloidal model systems: visualizing crystal nucleation pathways during liquid-to-solid transition and visualizing low-frequency quasi-localized vibrational modes in disordered solids.
On the first topic, we developed a new method for bond order analysis to identify various local symmetries and applied it to illustrate kinetic pathways in colloidal crystallization. Our new analysis reveals multiple-symmetry precursors and nuclei, as well as two cross-symmetry transformation pathways among them. It also illustrates the density-symmetry decoupling in the crystallization of soft-potential colloids. Our study clarifies the properties of intermediate nucleation structures and brings new insights to the kinetic pathways of crystal nucleation
On the second topic, we illustrated the origin of quasi-localized low-frequency vibrational modes in amorphous solids. By directly visualizing vibrational modes in disordered colloidal systems, we discovered strong coupling between transverse excitations and defective structures, which explains the origin of the quasi-localized low-frequency modes.
Reference
1) Peng Tan, Ning Xu and Lei Xu, Nature Physics 10, 73-79 (2014)
2) Peng Tan, Ning Xu, Andrew B. Schofield and Lei Xu, Phys. Rev. Lett. 108, 095501 (2012) |
