Origin of anomalous magnetotransport in kagome superconductors AV$_{3}$Sb$_{5}$ (A=K,Rb,Cs)
Multiple anomalous features in electronic spectra of metals with kagome lattice structure -- van Hove singularities, Dirac points, and flat bands -- imply that materials containing this structural motif may lie at a nexus of topological and correlated electron physics. Due to the prospects of such exceptional electronic behavior, the recent discovery of superconductivity coexisting with charge-density wave (CDW) order in the layered kagome metals AV$_{3}$Sb$_{5}$ (A=K,Rb,Cs) has attracted considerable attention. Notably, these kagome metals express unconventional magnetotransport behavior, including a linear-in-H diagonal resistivity at low fields, and an even more peculiar, nonmonotonic sign-changing behavior of the Hall resistivity, which has been speculated to arise from a chiral CDW. We argue here that this unusual magnetotransport derives not from such unconventional phenomena, but rather from the unique fermiology of the AV$_{3}$Sb$_{5}$ materials. Specifically, it is caused by a large, concave hexagonal Fermi surface sheet formed in the close proximity to the van Hove singularities, which is backfolded into a small hexagonal sheet and two large triangular sheets in the CDW state. We introduce a model of the electronic structure of these Fermi surface sheets that allows for a full analytical treatment within Boltzmann kinetic theory and that enables semi-quantitative fits of our transport data. Specifically, we find that the anomalous magnetotransport behavior is caused by the confluence of strong reduction of the Fermi velocity near the van Hove singularities located near the vertices of the hexagonal sheet and sharp corners in Fermi surface generated by the CDW reconstruction.