Advances of polar and multiferroic skyrmion

Complex topological configurations in condensed matter physics
provide a fertile ground for the exploration of novel emergent phenomena
and exotic phases. Recent discoveries of polarization vortices, flux
closures, and phase coexistence in ferroelectric oxide superlattices under
applied fields have revealed new opportunities for studying topological
behavior and manipulating these features with electric fields [1,2]. In
this talk, we demonstrate the transition from room-temperature
ferroelectric flux closures to polar vortices and skyrmions in lead
titanate layers confined by strontium titanate layers through epitaxial
engineering [3]. Phasefield modeling and second-principles calculations
confirm that polar vortices carry a topological charge of zero, while
polar skyrmions have a charge of +1 [4]. Additionally, these
nanometer-scale polar structures can be controlled via electric fields and
temperature modulation. We also observe self-assembled topological
nanostructures in multiferroic BiFeO3, which can be further manipulated by
electric fields. Importantly, applying a small voltage generates high
domain wall currents suitable for resistive memory applications, and a
notable magnetic moment is detected from these self-assembled structures,
offering promise for high-frequency electronics and memory technologies.

References:

[1] Yadav, A.K., Nelson, C.T. et al., Observation of polar vortices in
oxide superlattices. Nature 530, 198-201 (2016).
[2] Damodaran, A., Clarkson, J., Hong, Z., Liu, H. et al., Phase
coexistence and electric-field control of toroidal order in oxide
superlattices. Nat. Mater. 16, 1003 (2017).
[3] Das, S et al, Observation of room temperature polar skyrmions. Nature
568, 368-372 (2019).
[4] Li, Q., Das, S. et al, Collective excitations of polar vortices.
Nature 592, 376-380 (2021).