Loop current Chern metal, roton superconductivity, and charge-6e flux quantization in kagome metals and superconductors

Speaker

Prof. Ziqiang Wang

Boston College

Time

3：00pm, March 7, 2025

Place

Conference room on 3F, Material Science and Research Building

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.

Prof. Wang has over 210 publications, including over 50 in Nature and Nature branded journals and over 50 in the Physical Review Letters. His current research focuses on the fundamental physics of correlated and topological electronic states in quantum materials, including unconventional superconductors, quantum magnetism, integer and fractional quantum anomalous Hall systems, topological superconductors and other extraordinary forms of superconducting and vortex matter.

Abstract

The newly emerged kagome superconductors AV₃Sb₅ (A=K, Cs, Rb) exhibit a cascade of correlated and topological quantum states. We discuss recent experimental evidence for time-reversal symmetry breaking in both the normal and the superconducting state. We argue that the essential phenomenology can be captured by an unconventional charge density wave (CDW) with loop current order, realizable in models with extended Coulomb interactions on the kagome lattice. This leads to a loop current Chern metal with a partially filled Chern band and Chern Fermi pockets carrying concentrated Berry curvature. We show how Cooper pairing over the Chern Fermi pockets produces a novel roton superconductor, where the internal phases of three pairing components are locked at 120-degrees and loop supercurrents circulate around an emergent vortex-antivortex lattice with pair density modulations. We discuss the extraordinary properties of this intrinsic chiral topological superconductor and the possible emergence of charge-6e superconductivity in connection to the experimental observation of charge-6e flux quantization.