Boston College

报告摘要：

In ordinary superconductors, an external magnetic field is needed to generate magnetic vortices. We discuss two examples where this conventional folklore breaks down. The first example is superconductors with strong spin-orbit coupling. We show that topological defect excitations, dubbed quantum anomalous vortex (QAV), can nucleate around magnetic ions spontaneously in the absence of external magnetic fields. When such superconductors possess a topological band structure, as do certain Fe-based superconductors, the magnetic impurity induced QAV is nonabelian and hosts Majorana zero mode (MZM) in the vortex core. Recent observations of QAV and MZM will be discussed. The second example concerns nonmagnetic kagome superconductors AV3Sb5 (A=K, Cs, Rb). There is experimental evidence for time-reversal symmetry (TRS) breaking, despite the absence of spin-related magnetism. We argue that the essential phenomenology can be captured by an unconventional charge density wave (CDW) with persistent electric loop current order. This leads to a Chern metal with a partially filled Chern band and Fermi pockets of concentrated Berry curvature. We show Cooper pairing on these Chern Fermi pockets produces a novel roton superconductor, where the internal phases of three pairing components are locked at 120 degrees, forming an emergent vortex-antivortex lattice. We discuss properties of the chiral topological roton superconductor and the possible emergence of charge-6e superconductivity in connection to recent experimental evidence for chiral kagome superconductors, exhibiting pair density modulations, zero-field superconducting diode effect, and charge-6e flux quantization.

报告人简介：

Ziqiang Wang graduated from Tsinghua University in 1984 and received his Ph.D. degree in Physics from Columbia University in 1989. He was a postdoc fellow at Rutgers University and Los Alamos National Laboratory, and became an assistant professor at Boston University in 1993. He is currently a professor in the Physics Department at Boston College. He received a Cottrell Scholar Award in 1996 and a SEED Award in 2021 from Research Corporation for Science Advancement. He is an elected fellow of the American Physical Society.

报告地点：M236会议室

联系人： 李世亮 研究员