Seminar Dr. Leo Boron - Topological polar phases in ferroelectric nanowires

The last decade new topological states have been discovered in nanoscale ferroelectrics
challenging the idea of uniformity in these types of systems. While a variety of topological
states are now reasonably well understood in two-dimensional (2D) ferroelectric
heterostructures, there are significant ongoing efforts to comprehensively understand lower
dimensional ferroelectric configurations. Only a few studies considered 1d ferroelectric
nanowires and nanotubes.
A strain-temperature and a radius-temperature phase diagrams for PbTiO3 nanowires were
obtained through three different approaches: a second principles atomic-level approach, a
phenomenological Ginzburg-Landau-Devonshire model and the phase field method.
Various topological polarization states were discovered in the nanowires, including the vortex
state with polarization swirling around the nanowire’s c axis, the helical state with the
polarization screwing along the c axis and the uniform polarization state extending along the
c axis. Furthermore, we observed a strong size effect resulting in polar texture which is
attributed to the role of surface tension.
We provide an overview of the unique physical properties discovered in ferroelectric
nanowires. These properties are important for applications. For instance the helix phase
holds great interest for optoelectronics and quantum communication technologies. The
switching between different topological states can be implemented for a multilevel logic
element in non-von-Neumann computing circuits.