CAMP Seminar: Nanoscale Dynamics of Ferroelectric Domains and Domain Walls
The low-energy collective response of solids to external stimuli carries important information on the system dynamics. In ferroelectric materials, for instance, it is generally believed that the dielectric dispersion in the radio-frequency range is associated with the domain wall (DW) dynamics, although the physical origin remains controversial after six decades of research. Using a broadband (from 1 MHz to 10 GHz) scanning impedance microscope, we show that the effective conductivity at microwave frequencies of certain ferroelectric DWs can be many orders of magnitude higher than the dc conductivity in the bulk crystals. First-principles-based model calculations reveal the presence of a localized GHz-regime phonon mode that corresponds to the DW vibration around its equilibrium position. The probe tip can also surface acoustic waves, resulting in interference patterns observed in the microwave images. Our results pave the way to probe various phenomena of elastic waves in complex quantum materials by nanoscale electromagnetic imaging.