Polarization Vortices in a Ferromagnetic Metal via Twistronics

TL;DR

This paper demonstrates that twisting in a ferromagnetic metal can create polarization vortices linked to moire patterns, revealing new ways to manipulate electronic and magnetic properties in metallic systems.

Contribution

It introduces the concept of polarization vortices in a ferromagnetic metal induced by moire engineering, expanding polarization topology design into metallic materials.

Findings

Twisted stacking induces dipolar vortices in SrRuO3 membranes.

Polarization vortices depend on the twist angle and are linked to moire-periodic flexoelectricity.

Multiferroic behavior emerges below the Curie temperature, with polarization and ferromagnetism showing opposite twist-angle dependencies.

Abstract

Recent advances in moire engineering provide new pathways for manipulating lattice distortions and electronic properties in low-dimensional materials. Here, we demonstrate that twisted stacking can induce dipolar vortices in metallic SrRuO3 membranes, despite the presence of free charges that would normally screen depolarizing fields and dipole-dipole interactions. These polarization vortices are correlated with moire-periodic flexoelectricity induced by shear strain gradients, and exhibit a pronounced dependence on the twist angle. In addition, multiferroic behavior emerges below the ferromagnetic Curie temperature of the films, whereby polarization and ferromagnetism coexist and compete, showing opposite twist-angle dependencies of their respective magnitudes. Density functional theory calculations provide insights into the microscopic origin of these observations. Our findings extend the scope of polarization topology design beyond dielectric materials and into metals.