报 告 人：万贤纲
报告题目：Novel Superconductivity Induced by Electron-Phonon Interaction
报告时间：2022年8月8日（周一），上午10：00
报告地点：物电学院重点实验室428会议室，腾讯会议号：906871326
主办单位：物理与电子工程学院、科学技术研究院
报告人简介：
南京大学物理学院教授，1990年至2000年在南京大学学习，获得学士、硕士、博士学位。2001起在南京大学历任讲师，副教授，2010年任教授。主要学术成绩为：提出了新型拓扑量子态—Weyl半金属,该工作入选美国物理学会PRB期刊创刊50年“里程碑”(MILESTONE)文章，评语是：提出了一种新的量子物质状态外尔半金属(The Weyl semimetal, a new state of quantum matter, is proposed.)；发展了一套计算磁性相互作用的方法并确定多个复杂体系的基态磁构型；基于原子绝缘体基组发展了高效判断拓扑性能的理论方法，并用其对无机材料数据库里面所有非磁材料的拓扑特性进行了分类。2015年获得“国家杰出青年科学基金”，先后获得崔琦物理学奖，叶企孙物理奖、腾讯基金会科学探索奖、全国创新争先奖。
报告摘要：
1) We discuss the electronicstructure, lattice dynamics, and electron-phonon interaction of the newlydiscovered superconductor LaO0.5F0.5BiS2 using density-functional-based calculations.A strong Fermi surface nesting at k = (π,π,0) suggests a proximity tocharge-density-wave instability and leads to imaginary harmonic phonons at this k point associated within-plane displacements of S atoms. Total energy analysis resolves only ashallow double-well potential well preventing the appearance of staticlong-range order. Both harmonic and anharmonic contributions to electron-phononcoupling are evaluated and give a total coupling constant λ=0.85, prompting this material to be a conventionalsuperconductor contrary to structurally similar FeAs materials.
2) Understanding exotic,non-s-wave-like states of Cooper pairs is important and may lead to newsuperconductors with higher critical temperatures and novel properties. Theirexistence is known to be possible but has always been thought to be associated withnon-traditional mechanisms of superconductivity where electronic correlationsplay an important role. Here we use a first principles linear responsecalculation to show that in doped topological insulator an unconventionalp-wave-like state can be favoured via a conventional phonon-mediated mechanism,as driven by an unusual, almost singular behaviour of the electron–phononinteraction at long wavelengths. This may provide a new platform for ourunderstanding of superconductivity phenomena in doped band insulators.