时间：2021年11月9日（周二） 14:00-15:30

Time：14:00-15:30, Tuesday, November 9th, 2021

主持人: 西湖大学理学院PI 李牮 博士

Host：Dr. Jian Li, PI of School of Science, Westlake University

地点：西湖大学云栖校区4号楼311会议室

Venue：Room 311, Building 4, Yunqi Campus

主讲嘉宾/Speaker：

万贤纲 教授

Prof. Xian-Gang Wan

教授，南京大学物理学院

Professor, School of Physics, Nanjing University

主讲人简介/Biography:

南京大学物理学院教授、博士生导师。研究方向主要采用第一性原理和有效模型相结合的手段研究具有强自旋轨道耦合的关联电子体系。因在烧绿石结构 Ir 氧化物中预言新奇 Weyl 半金属态的理论工作及相关第一性原理电子结构计算物理研究而获得 2014 年度香港大学 Daniel Tsui(崔琦) Fellowship。2015年获得国家杰出青年科学基金。

讲座摘要/Abstract:

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.

讲座联系人/Contact:

理学院 陈老师 chenkeyu@westlake.edu.cn