Flat Band Induced Negative Magnetoresistance in Multi-Orbital Kagome Metal

TL;DR

This paper demonstrates that flat bands in a multi-orbital kagome metal CoSn lead to negative magnetoresistance and ferromagnetic fluctuations, revealing correlation effects that could enable new quantum states.

Contribution

It provides the first evidence of flat band-induced correlation effects in a multi-orbital bulk kagome metal, combining experimental and theoretical analysis.

Findings

Observation of negative magnetoresistance in CoSn

Signature of ferromagnetic fluctuations near flat band

Correlation effects modulated by Fermi level tuning

Abstract

Electronic flat band systems are a fertile platform to host correlation-induced quantum phenomena such as unconventional superconductivity, magnetism and topological orders. While flat band has been established in geometrically frustrated structures, such as the kagome lattice, flat band-induced correlation effects especially in those multi-orbital bulk systems are rarely seen. Here we report negative magnetoresistance and signature of ferromagnetic fluctuations in a prototypical kagome metal CoSn, which features a flat band in proximity to the Fermi level. We find that the magnetoresistance is dictated by electronic correlations via Fermi level tuning. Combining with first principles and model calculations, we establish flat band-induced correlation effects in a multi-orbital electronic system, which opens new routes to realize unconventional superconducting and topological states in geometrically frustrated metals.