Speaker: Dr. Haidan Wen, X-ray Science Division, Argonne National Laboratory
Title: Terahertz-field-driven collective dynamics in topological ferroelectric nanostructures
Abstract: New classes of nanoscale ferroelectric structures with nontrivial topological properties have been recently discovered, including polar vortices and skyrmions. These electrical counterparts of magnetic systems can host new collective dynamics and functionality that result from the unique connectivity of polarizations, holding promises for electric-field control of topological structures for data processing with ultrahigh speed and density. However, their dynamics are unknown. In this talk, I will present our recent work to reveal collective dynamics in polar vortices by terahertz-field-pump, femtosecond x-ray diffraction techniques [1]. We reveal a soft mode in which nanoscopic circular with the picosecond oscillating vorticity, arising from complex many-body interactions between the polar order and lattice. The condensation of its dynamics at a critical strain indicates a new phase transition in polar vortices. The discovery of this tunable soft mode opens a new avenue for high-frequency dielectrics and optoelectronics applications. Looking into the future, the upgraded APS with enhanced x-ray coherent flux open opportunities to visualize the dynamical atomic displacement of these novel collective excitations in ferroelectric nanostructures with unprecedented precision.
[1] Q. Li, V. A. Stoica, et al. "Subterahertz collective dynamics of polar vortices", Nature, 592, 376-380 (2021)
Bio: Dr. Wen is a Physicist in the X-ray Science Division at Argonne National Laboratory. Prior to his current position, he was a research associate at SLAC National Laboratory and Stanford University. He received his Ph.D. in physics from the University of Michigan, Ann Arbor, in 2006 and B.S. from the University of Science and Technology of China in 2001. Dr. Wen’s research focuses on investigating ultrafast dynamics of multiple degrees of freedom such as lattice, charge, and magnetic orders in quantum materials, by using a wide range of electromagnetic radiation including THz, optical, and X-ray pulses. He is interested in the phenomena that occur on nanometer to micrometer length scales where the energy conversion and transport are influenced by novel boundary conditions, collective dynamics, and mesoscale effects. He is developing advanced spatiotemporally resolved characterization techniques by integrating various x-ray microscopy and optical microscopy to tackle challenges of measuring and understanding nanoscale energy transport and conversion in the dynamical processes of phase transition, nanoscale thermal transport, nanoscale structure-property correlation.
Where: https://bluejeans.com/920655450
Phone Dial-in: +1.312.216.0325 (US (Chicago))
Meeting ID: 920 655 450