Charge-density wave transition in magnetic topological semimetal EuAl$_4$

TL;DR

This study investigates how charge-density wave (CDW) order influences the topological and magnetic properties of EuAl$_4$, revealing that CDW can destabilize magnetism and promote chiral spin textures through band structure modifications.

Contribution

It provides a comprehensive analysis combining optical spectroscopy and first-principles calculations to elucidate the role of CDW in magnetic topological semimetals.

Findings

CDW induces a partial gap and enhances mid-infrared absorption.

CDW affects band structure, destabilizing antiferromagnetic interactions.

CDW promotes chiral spin textures by mediating anisotropic magnetic interactions.

Abstract

The interplay among topology, charge-density wave (CDW), and magnetism can give rise to a plethora of exotic quantum phenomena. Recently, a group of magnetic topological semimetals with tetragonal lattices and CDW order were found to exhibit anomalous magnetic instability, helical spin ordering, and the presence of skyrmions. However, the underlying mechanism responsible for these observations remains unclear. Here, we conducted a comprehensive investigation into the impact of CDW on the topological and magnetic properties of EuAl$_4$ using optical spectroscopy and the first-principles calculations. Through optical spectroscopy, we observed a partial gap (60~meV) on the Fermi surface and an enhanced mid-infrared absorption around 0.4~eV after the CDW transition. Magneto-optical spectroscopy and the first-principles calculations proved that, by affecting the band structure, the CDW order frustrates the antiferromagnetic interactions but strengthened the ferromagnetic ones, which can destabilize the magnetism. With lower symmetry in the CDW ordered state, carriers from the Weyl bands will mediate the anisotropic magnetic interactions promoting the formation of chiral spin textures. Conversely, without the CDW order, the counterpart EuGa$_4$ shows robust collinear antiferromagnetic order. Our findings uncover the pivotal role played by CDW order in arousing intricate magnetism in topological materials and provide valuable insights into controlling topological and magnetic properties through the manipulation of CDW orders.