Speaker: Professor Wan Xiangang
Topic: Novel Superconductivity Induced by Electron-Phonon Interaction
Date: August 8, 2022
Time: 10:00 a.m.
Venue: Key Laboratory 428, Building 8
Tencent Meeting ID: 906-871-326
Sponsor: School of Physics and Electronic Engineering, Institute of Science and Technology
Brief Introduction of the Speaker:
Professor Wan Xiangang works in the School of Physics, Nanjing University. He studied at Nanjing University from 1990 to 2000 and obtained bachelor, master, and doctorate degrees respectively. Since 2001, he has been a lecturer and then associate professor in Nanjing University. In 2010, he became a professor. His work was selected into the 50-year milestone article of Physical Review B.,which remarks that the Weyl semimetal, a new state of quantum matter, is proposed. In 2015, he won the The National Science Fund for Distinguished Young Scholars, the Daniel Tsui Fellowship, Chi-Sun Yeh Fellowship, Xplorer Prize, and the National Innovation Award.
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 within-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 an harmonic 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.