Abstract

There has been much interest in topological defects of spontaneous polarization as templates for unique physical phenomena and in the design of electronic devices. Experimental investigations of the complex topologies of polarization have been limited to surface phenomena, which has restricted the probing of the dynamic volumetric domain morphology in operando. I will discuss the behavior of three-dimensional vortices formed due to competing interactions involving ferroelectric domains observed by Bragg coherent diffractive imaging. I will show results for a single BaTiO3 nanoparticle of size ~100 nm in a composite polymer/ferroelectric capacitor, and discuss the structural phase transitions under the influence of an external electric field, including a mobile vortex core exhibiting a reversible hysteretic transformation path and changes in toroidal moment. Results and extensions to magnetic ferroelectrics such Barium Hexaferrite, as well as some recent results on observations of varied topological relics including strings will be pointed out.

Biography

Dr. Edwin Fohtung is an Associate Professor at Rensselaer Polytechnic Institute in New York. He received his Ph.D. ( Dr. rer. nat., summa cum laude) from the University of Freiburg, Germany in 2010. Before he joined Rensselaer Polytechnic as Faculty in 2019 he was the LANSCE (Los Alamos Neutron Science Center) Professor of physics at Los Alamos National Laboratory and New Mexico State University. Before this, he was a postdoctoral fellow with the Department of physics at the University of California San Diego in the Shpyrko Group and worked at the Institute for Photon Science and Synchrotron Radiation in Karlsruhe Institute of Technology (KIT) in Germany. Prof. Fohtung earned his B.Sc. (2005) and M.Sc. (2007) in Technical and Applied Physics from the St. Petersburg State Polytechnic University Russia. Prof. Fohtung is particularly interested in nanoscale structure, fluctuations, and dynamics arising due to coupled and competing spin, orbital, charge, and lattice degree of freedom. To interrogate such order parameters in a variety of condensed matter systems, the Fohtung Research group develops novel synchrotron-based coherent x-ray and neutron scattering techniques. Professor Fohtung is the recipient of numerous awards including the LANSCE Professorship and Rosen Fellow at Los Alamos National Laboratory. He is also the recipient of multiple grants from the US Department of Defense, Airforce of Office of Scientific Research (DoD-AFOSR), the National Nuclear Security Administration (NNSA), the National Science Foundation (NSF) and other LANL directed research and development program awards. Professor Fohtung is currently a visiting professor at Lund University and a LINXS (Lund Institute of Advanced Neutron and X-ray Science) fellow in Lund Sweden.