Complex magnetic and spatial symmetry breaking from correlations in kagome flat bands

TL;DR

This paper explores the complex magnetic phases and symmetry breaking in kagome flat bands due to electron correlations, revealing diverse magnetic orders and potential spin liquid states through mean-field and symmetry analysis.

Contribution

It provides a comprehensive phase diagram of correlated electrons in kagome flat bands, including unconventional magnetic orders and spin liquids, supported by theoretical analysis and experimental comparison.

Findings

Identification of cascades of unconventional magnetic orders

Mapping of phase diagram under extended repulsion

Comparison with experiments on FeSn and FeGe

Abstract

We present the mean-field phase diagram of electrons in a kagome flat band with repulsive interactions. In addition to flat-band ferromagnetism, the Hartree-Fock analysis yields cascades of unconventional magnetic orders driven by onsite repulsion as filling changes. These include a series of antiferromagnetic (AFM) spin-charge stripe orders, as well as an evolution from $120^\circ$AFM to intriguing noncoplanar spin orders with tetrahedral structures. We also map out the phase diagram under extended repulsion at half and empty fillings of the flat band. To examine the possibilities beyond the mean-field level, we conduct a projective symmetry group analysis and identify the feasible $\mathbb Z_2$ spin liquids and the magnetic orders derivable from them. The theoretical phase diagrams are compared with recent experiments on FeSn and FeGe, enabling a determination of the most likely magnetic instabilities in these and similar flat-band kagome materials.