Correlated order at the tipping point in the kagome metal CsV$_3$Sb$_5$

TL;DR

This study reveals that in highly symmetric CsV$_3$Sb$_5$ kagome metal, in-plane transport anisotropy emerges only under weak magnetic fields or strains, suggesting flux order coexists with bond order and clarifies charge order symmetry.

Contribution

The paper demonstrates that flux order can be induced by magnetic fields or strain in CsV$_3$Sb$_5$, unifying previous controversies about charge order symmetries in kagome metals.

Findings

No anisotropy in pristine samples at any temperature.

In-plane anisotropy appears under weak magnetic fields or strain.

Flux order coexists with bond order, induced by magnetic field.

Abstract

Spontaneously broken symmetries are at the heart of many phenomena of quantum matter and physics more generally. However, determining the exact symmetries broken can be challenging due to imperfections such as strain, in particular when multiple electronic orders form complex interactions. This is exemplified by charge order in some kagome systems, which are speculated to show nematicity and flux order from orbital currents. We fabricated highly symmetric samples of a member of this family, CsV$_3$Sb$_5$, and measured their transport properties. We find the absence of measurable anisotropy at any temperature in the unperturbed material, however, a striking in-plane transport anisotropy appears when either weak magnetic fields or strains are present. A symmetry analysis indicates that a perpendicular magnetic field can indeed lead to in-plane anisotropy by inducing a flux order coexisting with more conventional bond order. Our results provide a unifying picture for the controversial charge order in kagome metals and highlight the need for microscopic materials control in the identification of broken symmetries.