Instability of the charge density wave in Kagome magnet FeGe

TL;DR

This study reveals the fragility and complex disruption process of charge density waves in FeGe Kagome metal, combining STM experiments with first-principles calculations to understand competing CDW instabilities and their relation to magnetism.

Contribution

It uncovers the transient and coexistence phenomena of CDWs in FeGe, highlighting the strong instability of the CDW ground state due to phonon mode softening and competing phases.

Findings

2*2 CDW is fragile and easily disrupted

Coexistence of sqrt3*sqrt3 and 2*2 CDWs in samples

Presence of intermediate CDW states during disruption

Abstract

Kagome metals show rich competing quantum phases due to geometry frustration, flat bands, many-body effects, and non-trivial topology. Recently, a novel charge density wave (CDW) was discovered deep inside the antiferromagnetic phase of FeGe, attracting intense attention due to close relation with magnetism. Here, via a scanning tunneling microscope (STM), we find the 2*2 CDW in FeGe is very fragile and can be readily disrupted into the initial 1*1 phase; Small sqrt3*sqrt3 CDW puddles are found to coexist with the 2*2 CDW in as-grown samples, and can also be induced in the intermediate process of CDW disruption, which will eventually transform into the initial 1*1 phase. Moreover, an exotic intermediate CDW state and standalone CDW nuclei appear unexpectedly during the disruption process. Our first-principle calculations find equal softening of a flat optical phonon mode in a large momentum region around the CDW wave vector, corresponding to numerous competing CDWs with close energies. This might lead to strong instability of the CDW ground state, responsible for STM observations. Our findings provide more novel experimental aspects to understand the CDW in FeGe and suggest FeGe-like Kagome metals are ideal platforms for studying the physics of competing CDW instabilities.