应兰州大学物理科学与技术学院和光转换材料与技术国家地方联合工程实验室邀请，美国犹他大学刘锋教授将于7月3-4日间来我校访问并面向全校师生及功能与环境材料研究所做学术报告，敬请关注并欢迎大家参加！

刘锋教授简介：

刘锋，美国犹他大学材料工程系教授，系主任，1984年获得清华大学核材料物理专业学士，1990年获得美国弗吉尼亚联邦大学化学物理专业博士。刘锋教授入选美国物理学会学士（APS Fellow），物理学顶级期刊Phys.Rev.Lett.编辑，中科院海外知名学者。研究领域包括纳米结构理论、纳米材料和器件、表面与界面和薄膜生长机制及计算材料物理等，是有机拓扑材料和制备半导体表面拓扑相的发明人，也是应变引导的纳米结构自组装和纳米力学构筑领域的主要开拓者之一。发表文章280余篇， 拥有10多项专利，20余章丛书和20余篇邀请综述。

报告一：Epitaxial Growth of Dirac and Topological Overlayer on Semiconductor Surface and Strain Engineering

时间：2018年7月3日（星期二）16:00-17:30

地点：格致楼3016会议室

摘要：

Since the discovery of graphene, 2D materials, such as 2D Dirac and topological materials, have attracted tremendous interest because they offer a new platform for next-generation of electronic, optoelectronic, spintronic and valleytronic devices with distinctive properties different from their 3D bulk counterparts. Most 2D materials are theoretically predicted in the freestanding form. But the freestanding 2D atomic layers are generally metastable and their intrinsic properties may be altered when they are transferred onto a substrate, which is often required for measurement as well as for eventual device fabrication. In this talk, I will present our recent studies to explore a novel approach of surface-based 2D Dirac and topological materials by direct epitaxial growth of metal overlayers on a semiconductor substrate without transfer process, using first-principles calculation combined with tight-binding model analysis. Specifically, I will discuss several examples demonstrating formation of Dirac, quantum spin Hall and quantum anomalous Hall states in the Si(111), Ge(111) surfaces. Furthermore, I will discuss an interesting approach to manipulate edge spin current of a quantum spin Hall insulator by bending strain engineering. Our findings may greatly broaden the scientific scope and technological impact of emerging 2D Dirac and topological materials.

报告二：From Type III Dirac Fermion to Black Hole Hawking Radiation

时间：2018年7月4日（星期三）9:00-10:30

地点：格致楼3016会议室

摘要：

Topological semimetals host interesting new types of fermions as low-energy quasiparticles. They not only exhibit novel physical properties, but also offer a versatile platform for simulating relativistic particles of high-energy physics as well as “new particles” that have no counterparts in high-energy physics. Recently, realizing new fermions, such as type-I and type-II Dirac/Weyl fermions in condensed matter systems, has attracted considerable attention. I this talk, I will show that the transition state from type-I to type-II Dirac fermions can be viewed as a type-III Dirac fermion, which exhibits unique characteristics, such as a Dirac-line Fermi surface with nontrivial topological invariant and critical chiral anomaly effect, distinct from previously known Dirac semimetals. Most interestingly, we propose a solid-state analog of the black hole event horizon by engineering topological phase transition in between the type I, II and III Dirac fermions. We demonstrate such analogue using the intrinsic Dirac states in strained inhomogeneous Zn2In2In5 and the laser induced Floquet-Dirac states in black phosphorous to simulate black hole evaporation with an unprecedented high Hawking temperature.

报告三：Experience Sharing of Scientific Research and Defect and Surface Calculation.

时间：2018年7月4日（星期三）10:30-11:30

地点：格致楼3016会议室

摘要：

在这场报告中，刘锋教授将给大家分享一些科学研究方面的心得体会，并与大家交流关于缺陷和表面计算方面的内容。