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

Kavli Affiliate: Sol M. Gruner

| First 5 Authors: Kayla X. Nguyen, Yi Jiang, Michael C. Cao, Prafull Purohit, Ajay K. Yadav

| Summary:

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.

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