Probing the Fermi Surface Topology of Double-Layered Kagome Metals AV₆Sn₆ (A = Sc, Y) through Quantum Oscillations in Pulsed Magnetic Fields up to 91 T

Kagome lattice materials are known for hosting a variety of exotic physical phenomena, including geometrically frustrated magnetism, non-trivial band topology, flat electronic bands, charge density waves (CDW), and superconductivity. Here, using quantum oscillation measurements in pulsed magnetic fields up to 91 T, we investigate the electronic band structure underlying these correlated electronic behaviors in the double-layered Kagome systems: ScV₆Sn₆, which exhibits a CDW ground state and its isostructural counterpart YV₆Sn₆, which lacks the CDW. In YV₆Sn₆, our high-field data reveal a large electron pocket (≈ 67% of the Brillouin zone area) and a heavy cyclotron effective mass (≈ 2.8m₀), while in ScV₆Sn₆, signatures of zone folding are observed. The heavy effective mass confirms the presence of a van Hove singularity near the Fermi level in YV₆Sn₆, whereas the zone folding reflects the impact of CDW order in ScV₆Sn₆. Density functional theory (DFT) calculations of the electronic structure in YV₆Sn₆ show a Fermi surface for the unfolded Brillouin zone that closely corresponds to the experimental values for quantum oscillation frequency and cyclotron effective mass. For ScV₆Sn₆, DFT calculations on the folded Brillouin zone created by the CDW show a more complicated Fermi surface. Additionally, the Berry phases of the electron orbits, extracted from Landau level fan diagrams near the quantum limit, provide evidence for the non-trivial topology.