Superfluidity and superconductivity: their defeat, universal fluctuation, and respect to U(1) symmetry

顾威

上海交通大学

报告时间：2024年11月25日（周一）下午15:30

报告地点：紫金港校区段永平教学楼2号楼212报告厅

摘要：

Superfluidity and superconductivity are among the most exotic phenomena of certain quantum states of matter.  Their physical understanding, however, are primarily based on mean-field approximations that generate Bogoliubov-type number fluctuation, in direct contradiction to the strict number conservation of the system.  Based on rigorous analytical studies of quantum many-body systems, this talk will cover three fundamental issues against standard lore: 1) how to completely suppress quantum coherence in a homogeneous system to defeat superfluidity and produce the long-sought “quantum Bose metal”, 2) why the low-temperature fluctuation of modern superconductors irreparably invalidates standard theories and inspires qualitative correction to the standard theory of bosonic superfluidity, and 3) why superfluidity and superconductivity should not be regarded with spontaneously broken U(1) symmetry and why the zero modes in the vortex cores cannot be Majorana particles capable of braiding quantum information.

报告人简介：

After receiving his PhD degree from University of Tennessee at Knoxville in 2000, Professor Wei Ku conducted his postdoctoral research in University of California at Davis from 2001 to 2003.  He then worked as a staff scientist (Assistant Physicist, Associate Physicist, and Physicist) in Brookhaven National Laboratory and served as an Adjunct Professor in Stony Brook University since 2003, until he accepted the Zhiyuan Professor position in Shanghai Jiao Tong University in 2016.  In 2018, Professor Ku was appointed Deputy Director of the newly found Tsung-Dao Lee Institute in Shanghai, assisting Founding Director Frank Wilczek, the 2004 Nobel Laureate in Physics.  His main research area is theory and computation of condensed matter physics in real materials, with contributions mostly in the field of strongly correlated materials, unconventional superconductors, realistic effects of impurities, electronic excitations, and first-principles computational methods.  He has published more than 80 manuscripts, about half of which are in high-profile journals like the PNAS, Nature Physics, Phys. Rev. X, and Phys. Rev. Lett.  He is currently developing an “emergent Bose liquid” theory for strongly correlated materials, and applying it to the description of electronic structure of some unconventional superconductors.