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

8 Dec 2020  ·  Kayla X. Nguyen, Yi Jiang, Michael C. Cao, Prafull Purohit, Ajay K. Yadav, Pablo García-Fernández, Mark W. Tate, Celesta S. Chang, Pablo Aguado-Puente, Jorge Íñiguez, Fernando Gomez-Ortiz, Sol M. Gruner, Javier Junquera, Lane W. Martin, Ramamoorthy Ramesh, D. A. Muller ·

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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Materials Science Applied Physics