Oxide Superlattices: Balancing Polar Vortices and Stripes

A tuned oxide superlattice possesses two coexisting phases — one ferroelectric, the other with vortex order — which can be interconverted under electric field, changing material properties.

In our everyday experience we commonly observe vortices in fluids, from the swirl of milk in your coffee to the massive storm that ruins your weekend. However, vortices are also interesting phenomena in condensed-matter physics. For example, they are present in certain superconducting materials exposed to a magnetic field, or arise spontaneously during the formation of a Bose–Einstein gas, and are indicative of intriguing dynamics near a phase transition. Reporting in Nature Materials, Lane Martin and co-workers explore the coexistence of polarization vortices with other forms of polar ordering in finely layered perovskite oxides. To continue the imperfect analogy with fluids, this is similar to exploring how a river simultaneously has steady flow and whirlpools, and seeing how conditions affect whirlpool size and location. For a river, you cannot arrange different regions in an easily controllable and precise fashion — for polarization vortices, however, Martin and co-workers demonstrate that you can.