报告题目：Novel Superconductivity Induced by Electron-Phonon Interaction
报 告 人：万贤纲（教授，南京大学物理学院）
报告时间：2021年12月13日（星期一）上午10:00-11:30
报告地点：物理学院LE623
邀 请 人：王锐
报告人简介：
万贤纲，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。万贤纲教授提出了新型拓扑量子态—Weyl 半金属，引发了国际上Weyl 半金属的研究热潮；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。
万贤纲教授获得2014年度香港大学Daniel Tsui Fellowship；2015年获得国家杰出青年科学基金；2016年被评为教育部长江学者特聘教授；获中国物理学会2018-2019年度叶企孙物理奖；2019年获首届腾讯基金会“科学探索奖”；获2019年南京大学突出贡献奖；2020年获第二届全国创新争先奖。
报告摘要：
1) We discuss the electronic structure, lattice dynamics, and electron-phonon interaction of the newly discovered superconductor LaO0.5F0.5BiS2 using density-functional-based calculations. A strong Fermi surface nesting at k = (π,π,0) suggests a proximity to charge-density-wave instability and leads to imaginary harmonic phonons at this k point associated with in-plane displacements of S atoms. Total energy analysis resolves only a shallow double-well potential well preventing the appearance of static long-range order. Both harmonic and anharmonic contributions to electron-phonon coupling are evaluated and give a total coupling constant λ=0.85, prompting this material to be a conventional superconductor contrary to structurally similar FeAs materials.
2) Understanding exotic, non-s-wave-like states of Cooper pairs is important and may lead to new superconductors with higher critical temperatures and novel properties. Their existence is known to be possible but has always been thought to be associated with non-traditional mechanisms of superconductivity where electronic correlations play an important role. Here we use a first principles linear response calculation to show that in doped topological insulator an unconventional p-wave-like state can be favoured via a conventional phonon-mediated mechanism, as driven by an unusual, almost singular behaviour of the electron–phonon interaction at long wavelengths. This may provide a new platform for our understanding of superconductivity phenomena in doped band insulators.
