Electric-field control of emergent chirality in PbTiO3/SrTiO3 superlattices*

Novel chiral phases in ferroelectric materials—the polar analogs of magnetic vortices and skyrmions—can be stabilized in superlattices of PbTiO₃ and SrTiO₃. These chiral structures emerge in low-dimensional ferroelectrics, where the competition among gradient, electrostatic, and elastic energies favors non-uniform polarization configurations. Such phases can lead to new functional properties such as negative capacitance as well as unique interactions with polarized light. The characterization of these new phases and their three-dimensional chiral structure remains a challenge due to limitations of conventional electron microscopy and X-ray diffraction techniques.

In this talk, I will discuss how resonant soft X-ray diffraction (RSXD) can be used to study chirality in the emergent polarization textures (polar vortices and skyrmions) that form in PbTiO₃/SrTiO₃ superlattices. RSXD provides an element-specific probe with which to study the chiral configuration of orbitals in these materials. I will show that circular dichroism in RSXD originates from chiral arrays of electric quadrupoles, which are intrinsically related to the electric polarization. The presence of circular dichroism points to the formation of helical spirals of electric polarization, akin to Bloch domain walls in magnetic materials. Furthermore, circular dichroism can be observed in second harmonic generation. By performing electric-field dependent second harmonic generation circular dichroism experiments, we can demonstrate a coupling between the electric field and the handedness of chiral polar vortices.