Probing Microwave Dynamics of Ferroelectric Domain Walls

The past decade has witnessed the emergence and rapid development of domain wall (DW) nanoelectronics, which take advantage of the enhanced electronic conductivity at ferroelectric DWs due to the accumulation of free carriers. For practical high-speed electronics, however, the dielectric dispersion of ferroelectric materials at microwave frequencies has to be taken into account. Using a cohort of imaging techniques such as piezo-force microscopy, conductive atomic-force microscopy, and microwave impedance microscopy, we are able to determine the contribution of both mobile carriers and bound dipoles to the GHz response at ferroelectric domain walls. In LiNbO₃, BiFeO₃, and YMnO₃, the effective microwave conductivity of certain DWs is higher than that at DC by several orders of magnitude, while other walls behave the same at both DC and AC. First-principles and model calculations indicate that the AC-conductive DWs exhibit a localized vibrational mode, which can be excited by the alternating electric fields from the tip. In addition to the DW dynamics, the local electromechanical energy transduction in ferroelectric domains can also be visualized by the microwave probe. Our work opens up a new avenue to explore various phenomena in complex materials and novel devices by near-field electromagnetic imaging.

[1] X. Wu et al., Sci. Adv. 3, e1602371 (2017).
[2] X. Wu et al., Phys. Rev. B 98, 081409(R) (2018).
[3] L. Zheng et al., PNAS 115, 5339 (2018).