Origin of anomalous magnetotransport in kagome superconductors AV$_{3}$Sb$_{5}$ (A=K,Rb,Cs)

TL;DR

This paper explains the unusual magnetotransport phenomena in kagome superconductors AV$_{3}$Sb$_{5}$ by analyzing their Fermi surface topology and electronic structure, rather than invoking unconventional chiral charge-density waves.

Contribution

It introduces a detailed electronic structure model that accounts for the magnetotransport anomalies through Fermi surface features and CDW reconstruction effects.

Findings

Magnetotransport anomalies are due to Fermi surface topology and van Hove singularities.

A semi-analytical Boltzmann model fits the experimental transport data.

Fermi velocity reduction near van Hove points explains resistivity behavior.

Abstract

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.