Achievement

Mark Polking works on elucidating the fundamental nature of ferroelectric ordering in nanoscale structures. Using an NCEM microscope, he is examining atomic displacements in individual nanocrystals of GeTe and BaTiO3 in order to construct maps of the ferroelectric polarization patterns in these nanodots. Conflicting experimental and theoretical reports have suggested a complete disappearance of ferroelectric distortions, a disordered arrangement of local distortions analogous to a magnetic spin glass, or a toroidal polarization state in low-dimensional ferroelectrics. His results suggest that local ferroelectric distortions remain primarily linearly aligned, albeit with coherent rotations that diminish the overall magnitude of the polarization. The existence of these coherent rotations in both materials suggests that they arise via internal stresses imposed by the particle surfaces rather than via a depolarizing field resulting from unscreened polarization-induced surface charges.