Intertwined magnetism and charge density wave in a kagome metal
Electronic correlations are key sources of emergent orders in quantum materials. Kagome lattice is an intriguing platform system to realize interplays between quantum topology and electronic correlations. Flat bands introduced by destructive interference of valence band orbitals, Dirac crossings, and a pair of van Hove singularities (vHSs) have been suggested as key topological signatures in electronic structures are strongly connected to the kagome lattice. In addition, correlated emergent phases have been discovered among kagome metals including magnetism, charge density wave (CDW), nematicity, and superconductivity. These materials can be largely organized into two types: those that host magnetism or those that host CDW.Recently, we discovered a CDW phase in the magnetic kagome metal FeGe, providing a new platform for understanding the interplay between CDW and magnetism. The CDW in FeGe occurs at wavevectors identical to that of AV3Sb5, enhances the magnetic moment. Here, we utilized angle-resolved photoemission spectroscopy to observe all three characteristic electronic structure signatures of kagome lattices, namely flat bands, Dirac crossings, and vHSs. We also found a monotonic shift of the vHSs toward Fermi level as temperature increases by the evolution of magnetic exchange splitting. At the onset temperature of the CDW, we identify spectral gap formation at the Fermi level on the vHS-forming band, and nesting between them satisfies the CDW wavevectors observed by neutron scattering. Based on all the observations, we conclude that magnetic interaction drives band evolution, resulting in the CDW order. Hence, our work directly demonstrates an intertwined connection between the emergent flat-band magnetism and CDW driven by nesting between vHSs in the unique correlated kagome metal FeGe.
Host : Prof. Tae Won Noh