Transferring Orbital Angular Momentum to an Electron Beam Reveals Toroidal and Chiral Order

TL;DR

This study demonstrates that electric toroidal order in ferroelectric heterostructures can transfer measurable torque and orbital angular momentum to an electron beam, revealing complex chiral polarization patterns with potential for coupling ferroelectric and optical properties.

Contribution

It introduces a novel method using high-energy electron beams to detect and analyze electric toroidal order and chirality in ferroelectric materials, which was previously challenging.

Findings

Electric toroidal moments transfer torque and angular momentum to electron beams.

Polarization patterns in heterostructures are microscopically chiral.

Chirality enables potential coupling of ferroelectric and optical properties.

Abstract

Orbital angular momentum and torque transfer play central roles in a wide range of magnetic textures and devices including skyrmions and spin-torque electronics(1-4). Analogous topological structures are now also being explored in ferroelectrics, including polarization vortex arrays in ferroelectric/dielectric superlattices(5). Unlike magnetic toroidal order, electric toroidal order does not couple directly to linear external fields. To develop a mechanism that can control switching in polarization vortices, we utilize a high-energy electron beam and show that transverse currents are generated by polar order in the ballistic limit. We find that the presence of an electric toroidal moment in a ferro-rotational phase transfers a measurable torque and orbital angular momentum to the electron beam. Furthermore, we find that the complex polarization patterns, observed in these heterostructures, are microscopically chiral with a non-trivial axial component of the polarization. This chirality opens the door for the coupling of ferroelectric and optical properties.