Discovery of a long-ranged charge order with 1/4 Ge1-dimerization in an antiferromagnetic Kagome metal

TL;DR

This study reveals a long-ranged charge order with a specific 1/4 Ge1-dimerization in an antiferromagnetic Kagome metal, clarifying the nature of charge ordering and its structural implications in FeGe.

Contribution

It reports the discovery of a long-ranged charge order with a 2x2x2 superstructure and 1/4 Ge1-dimerization, resolving controversies about charge order mechanisms in FeGe.

Findings

Observation of a long-ranged charge order in FeGe.

Identification of a 2x2x2 superstructure with Ge1-dimerization.

Short-ranged charge order linked to occupational disorder at Ge1-sites.

Abstract

Exotic quantum states arise from the interplay of various degrees of freedom such as charge, spin, orbital, and lattice. Recently, a novel short-ranged charge order (CO) was discovered deep inside the antiferromagnetic phase of Kagome magnet FeGe, exhibiting close relationships with magnetism. Despite extensive investigations, the CO mechanism remains controversial, mainly because the short-ranged behavior hinders precise identification of CO superstructure. Here, combining multiple experimental techniques, we report the observation of a long-ranged CO in high-quality FeGe samples, which is accompanied with a first-order structural transition. With these high-quality samples, the distorted 2 * 2 * 2 CO superstructure is characterized by a strong dimerization along the c-axis of 1/4 of Ge1-sites in Fe3Ge layers, and in response to that, the 2 * 2 in-plane charge modulations are induced. Moreover, we show that the previously reported short-ranged CO might be related to large occupational disorders at Ge1-site, which upsets the equilibrium of the CO state and the ideal 1 * 1 * 1 structure with very close energies, inducing nanoscale coexistence of these two phases.Our study provides crucial clues for further understanding the CO properties in FeGe and helps to identify the CO mechanism.