The field of transition-metal kagome materials has leapt forward with the discovery of vanadium-based, nonmagnetic kagome superconductors AV₃Sb₅ (A=K, Cs, Rb). Central to the revelation is a cascade of correlated quantum states triggered by an unconventional 3Q charge density wave (CDW) order. We review recent experimental findings, focusing on evidence for time-reversal symmetry breaking in both the normal and the superconducting state. We argue that the essential phenomenology can be captured by a loop-current CDW order, realizable in models with extended Coulomb interactions on the kagome lattice. The loop-current Chern metal has a partially filled Chern band and Chern Fermi pockets carrying concentrated Berry curvature. We discuss how Cooper pairing over the Chern Fermi pockets produces a chiral topological superconductor with three pairing components whose relative phases are locked at 120-degrees, giving rise to a vortex-antivortex lattice of the novel roton pair density wave (PDW). Such a chiral state is frustrated on the kagome lattice and strong relative phase fluctuations suppress the true transition temperature, resulting in an extended region of superconducting fluctuations. We argue that charge-6e and charge-4e paired states, free of the chiral phase frustration, emerge over the extended fluctuation region upon melting of the charge-2e chiral superconductor, leading to fractionalized flux quantization and higher-charge superconductivity. The connections to the most recent experimental observations will be discussed. 

报告人简介：Professor Wang Ziqiang 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.

Prof. Wang has about 200 publications, including over 50 in the Physical Review Letters and over 40 in Nature and Nature branded journals. His current research focuses on the fundamental physics of correlated and topological electronic states in quantum materials, including unconventional superconductors, quantum magnetism, quantum Hall systems, topological superconductors and other extraordinary forms of superconducting matter.