Interplay of Charge Density Wave and Magnetism on the Kagom\'e Lattice

TL;DR

This paper investigates how charge density waves and magnetism interact on the kagomé lattice, revealing a complex interplay that leads to novel magnetic and topological phases, including a spin-polarized Chern insulator.

Contribution

It introduces a model demonstrating the emergence of bond-ordered charge density waves and loop-current states driven by Coulomb interactions at van Hove filling on the kagomé lattice.

Findings

Discovery of a ferromagnetic half-metal at large onsite U.

Identification of a bond-ordered CDW driven by intersite Coulomb interactions.

Observation of a spin-polarized Chern insulator exhibiting quantum anomalous Hall effect.

Abstract

Motivated by the recent discovery of charge density wave (CDW) order in the magnetic kagom\'e metal FeGe, we study the single-orbital $t$-$U$-$V_1$-$V_2$ model on the kagom\'e lattice, where $U$, $V_1$, and $V_2$ are the onsite, nearest neighbor, and next-nearest-neighbor Coulomb repulsions, respectively. When the Fermi level lies in the flat band, the instability toward ferromagnetic (FM) order gives rise to a FM half-metal at sufficiently large onsite $U$. Intriguingly, at band filling $n=17/24$, the Fermi level crosses the van Hove singularity of the spin-minority bands of the half-metal. We show that, due to the unique geometry and sublattice interference on the kagom\'e lattice at van Hove singularity, the intersite Coulomb interactions $V_1$ and $V_2$ drive a real and an imaginary bond-ordered $2a_0 \times 2a_0$ CDW instability, respectively. The FM loop current CDW with complex bond orders is a spin-polarized Chern insulator exhibiting the quantum anomalous Hall effect. The bond fluctuations are found to be substantially enhanced compared to the corresponding nonmagnetic kagom\'e metals at van Hove filling, providing a concrete model realization of the bond-ordered CDWs, including the FM loop current CDW, over the onsite charge density ordered states. When the spins are partially polarized, we find that the formation of bond-ordered CDWs enhances substantially the ordered magnetic moments. These findings provide physical insights for the emergence of loop-current and bond-ordered CDW and their interplay with magnetism on the kagom\'e lattice, with possible connections to the magnetic kagom\'e metal FeGe.