Frustrated charge density wave and quasi-long-range bond-orientational order in the magnetic kagome FeGe

TL;DR

This paper uncovers a dimerization-driven charge density wave in FeGe, revealing a precursor state with quasi-long-range bond-orientational order and topological defect-mediated melting, advancing understanding of frustrated kagome lattice systems.

Contribution

It identifies a novel precursor phase and elucidates the mechanism of the multiple-q CDW in magnetic kagome FeGe, highlighting the role of dimerization and topological defects.

Findings

Discovery of a dimerization-driven 2D hexagonal charge precursor.

Observation of anisotropic pretransitional charge fluctuations.

Evidence of topological defect-mediated melting of the CDW.

Abstract

The intrinsic frustrated nature of a kagome lattice is amenable to the realization of exotic phases of matter, such as quantum spin liquids or spin ices, and more recently the multiple-$\mathrm{\textbf{q}}$ charge density waves (CDW) in the kagome metals. Despite intense efforts to understand the mechanism driving the electronic modulations, its origin is still unknown and hindered by competing interactions and intertwined orders. Here, we identify a dimerization-driven 2D hexagonal charge-diffuse precursor in the antiferromagnetic kagome metal FeGe and demonstrate that the fraction of dimerized/undimerized states is the relevant order parameter of the multiple-$\mathrm{\textbf{q}}$ CDW of a continuous phase transition. The pretransitional charge fluctuations with propagation vector $\mathrm{\textbf{q}=\textbf{q}_M}$ at T$_{\mathrm{CDW}}$$<$T$<$T$^*$(125 K) are anisotropic, hence holding a quasi-long-range bond-orientational order. The broken translational symmetry emerges from the anisotropic diffuse precursor, akin to the Ising scenario of antiferromagnetic triangular lattices. The temperature and momentum dependence of the critical scattering show parallels to the stacked hexatic $\mathrm{B}$-phases reported in liquid crystals and transient states of CDWs and highlight the key role of the topological defect-mediated melting of the CDW in FeGe.