报告人：杨声远
新加坡科技设计大学助理教授
报告时间：2018年10月25日下午13:30-14:30
报告地点：行健楼437会议室
摘要：
Topological materials have been attracting great interest. Following the studies on topological insulators, the recent focus shifts towards the various topological metals (or semimetals), in which nontrivial band crossings appear near the Fermi level, endowing the low-energy electrons with novel emergent properties. In this talk, I discuss our two recent works, which proposed new types of topological metal states. The first is for semimetals with quadratic contact (Fermi) points (QCPs). We show that in the absence/presence of spin-orbit coupling, there may exist triply/quadruplydegenerate QCPs that are protected by symmetry. We reveal their unconventional Landau spectrum and their transformations under symmetry breaking. The second work is the discovery of the quadratic and cubic nodal lines. Around a nodal line, the dispersion for the energy difference between the bands is typically linear. We performed an exhaustive search over all 230 space groups for nodal lines with higher-order dispersions that can be stabilized by crystalline symmetry, and find that besides conventional linear nodal lines, there also exist lines with quadratic or cubic dispersions. Their signatures can manifest in a variety of physical properties such as the (joint) density of states, magneto-response, transport behavior, and topological surface states. Using ab-initio calculations, we identify possible material candidates that realize these exotic phases.
报告人简介：
杨声远，江苏省南京人。2001-2002年就读于清华大学电气自动化专业。2002-2005在香港大学修读数学物理专业，获理学学士。2005-2011年在得克萨斯大学奥斯汀分校修读凝聚态物理研究生，获博士学位。2011-2013年在休斯敦CGG Veritas US Services公司工作，任地质分析成像研究员。2013年起在新加坡科技设计大学担任助理教授。以往的研究课题包括磁性材料的磁动力学，二次谐波的发射理论，反常霍尔效应，二维材料/拓扑材料的物理性质。目前的研究方向包括拓扑半金属，拓扑绝缘体，二维材料的物理性质，电子晶体，自旋和谷电子学，量子输运等。
