UC Berkeley

This dissertation focuses on the study of complex oxide materials using synchrotron-based X-ray characterization techniques. Advanced synthesis methods allow oxide heterostructures to be built with atomic-layer precision, enabling the study of low-dimensional materials and creating a platform to easily manipulate key properties such as strain and electrostatic boundary conditions. Studies that focus on nanoscale heterostructures and emergent ordered phases require new techniques to study their properties, for which X-rays are invaluable. This work explores chiral polar textures (vortices and skyrmions) that emerge in ferroelectric/dielectric heterostructures and superlattices of PbTiO3/SrTiO3. To probe the structure and chirality of these phases, non-resonant hard X-ray diffraction and resonant soft X-ray diffraction are used. First, hard X-ray diffraction is used to characterize the structure of polar vortices and skyrmions. Next, to investigate chirality, resonant soft X-ray diffraction is used. Detailed circular dichroism measurements and reciprocal space scans are performed using resonant X-ray diffraction. Changes of the magnitude and sign of circular dichroism in reciprocal space reflect the three-dimensional structure of polar vortices and skyrmions. These structures have chiral arrays of electric dipole and quadrupole moments, and the scattering from these chiral arrays is modeled to reproduce the observations from resonant diffraction. Overall, this dissertation shows how the reciprocal space dependence of circular dichroism in resonant diffraction can be combined with theoretical modeling to sensitively probe the three-dimensional chiral structure of polar vortices and skyrmions. This technique can be extended to study ordered electric or magnetic phases in similar systems.