Strain-tunable charge localization coupled to complex magnetic orders in EuAl$_4$

Abstract

Charge localization is particularly interesting when coupled to antiferromagnetic spin structures. Coupled spin-charge orders are well established in elemental chromium and correlated oxide superconductors, yet the interplay between charge order and more complex magnetic textures -- such as skyrmion lattices and chiral spin structures -- remains largely unexplored. Here we report a comprehensive study of how charge localization couples to the unusually rich sequence of magnetic phases in EuAl$_4$. Using x-ray diffraction under applied magnetic field and uniaxial pressure, we demonstrate a direct coupling between the charge and spin order parameters. In the absence of external stimuli, charge localization is markedly enhanced upon entering the magnetically ordered phases. Strikingly, this effect is highly susceptible to strain: uniaxial pressure applied along the charge-order propagation direction further enhances localization, whereas pressure applied perpendicular to it weakens it. Application of magnetic field reveals both competitive and possible collaborative interactions between spin and charge ordering.This flexible coupling between spin and charge ordering opens a new route to designing symmetry-breaking states. Chiral charge order may for example be patterned from spin structures with that symmetry.