Non-Ising and chiral ferroelectric domain walls revealed by nonlinear optical microscopy
Résumé
The properties of ferroelectric domain walls can significantly differ from those of their parent
material. Elucidating their internal structure is essential for the design of advanced devices
exploiting nanoscale ferroicity and such localized functional properties. Here, we probe the
internal structure of 180° ferroelectric domain walls in lead zirconate titanate (PZT) thin films
and lithium tantalate bulk crystals by means of second-harmonic generation microscopy. In
both systems, we detect a pronounced second-harmonic signal at the walls. Local polarimetry
analysis of this signal combined with numerical modelling reveals the existence of a planar
polarization within the walls, with Ne´el and Bloch-like configurations in PZT and lithium
tantalate, respectively. Moreover, we find domain wall chirality reversal at line defects
crossing lithium tantalate crystals. Our results demonstrate a clear deviation from the ideal
Ising configuration that is traditionally expected in uniaxial ferroelectrics, corroborating recent
theoretical predictions of a more complex, often chiral structure.
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