The emergence of ferroelectric topological structures such as ferroelectric polarization vortices and polarization skyrmions in ferroelectric–dielectric superlattices (e.g., (PbTiO₃)ₙ/(SrTiO₃)ₙ, PTO/STO) is an important milestone in contemporary condensed matter physics and materials science. Polarization vortices are characterized by continuous polarization rotation around a vortex core, and their nanoscale size and ultrahigh theoretical storage density make them ideal candidates for next-generation high-density, low-energy-consumption nanoelectronic devices, with the potential to process sub-THz high-frequency signals in an energy-efficient manner. If these topological structures can be controllably manipulated, it is expected to fundamentally transform information storage and computing technologies and provide strong support for the rapid development of fields such as the Internet of Things, artificial intelligence, and large language models.

However, owing to the absence of the corresponding interaction mechanisms in ferroelectric materials and the strong coupling between polarization vortices and the lattice, real-time observation and controlled driving of polarization vortex motion under an electric field have not yet been realized. Vortex motion involves complex interactions with lattice distortions, defects, and external fields, making it highly sensitive to the surrounding environment and strongly pinned, so that precise control and manipulation are extremely difficult, which severely hinders its practical application. Although studies have demonstrated that structural defects such as dislocations can move back and forth under an applied electric field, whether electric fields can trigger deterministic controlled motion of topological defects such as polarization vortices remains a core challenge in this field and a prerequisite for realizing reconfigurable oxide nanoelectronics.

To address the above issues, a joint team composed of Zhejiang University, Hainan University, the Indian Institute of Science, and the University of California, Berkeley, among others, conducted an in-depth study using ZEPTOOLS' in situ TEM measurement system. By applying a direction-controllable local trailing electric field through a conductive atomic force microscopy tip, the team achieved, for the first time, deterministic, reversible, and reconfigurable controlled motion of polarization vortex boundaries in PbTiO₃/SrTiO₃ oxide heterostructures, and, with the help of in situ transmission electron microscopy and phase-field simulations, jointly confirmed its topologically protected motion mechanism driven by switching of the zigzag configuration of the vortex core.

Title: Controlled motion of polar vortex boundary in oxide heterostructures 
Journal: Nature Communications 
URL:http://dx.doi.org/10.1038/s41467-026-78049-z

This study first focused on the construction of high-quality PTO/STO heterostructures and the stabilization of a pure vortex phase. The research team grew a 5 nm SrRuO₃ buffer layer on a DyScO₃(001)ₚc single-crystal substrate and precisely prepared a 20 uc STO/20 uc PTO/20 uc STO trilayer structure by pulsed laser deposition assisted by reflection high-energy electron diffraction. X-ray diffraction and reciprocal space mapping confirmed the crystalline quality of the film and the regular vortex arrangement with an in-plane period of about ~14 nm, while atomic force microscopy confirmed the layer-by-layer growth mode and smooth surface morphology. Piezoresponse force microscopy and switching spectroscopy PFM measurements on a dense 50×50 grid clearly revealed the pure vortex phase and the spatial distribution of its switching behavior, and the results showed that the positive nucleation bias V_C⁺ and the average coercive bias V_C at the vortex boundaries are significantly lower than those of the vortex bulk, indicating that these regions are more sensitive to the trailing electric field and providing a key physical basis for driving vortex boundary motion with a low electric field.

On the above basis, the study focused on how to achieve deterministic motion of vortex boundaries under electric-field driving. The team used a conductive atomic force microscopy tip to apply a local trailing electric field along a predetermined path. After scanning along a specific path with a +5 V positive trailing electric field (50 nm/s), the original vortex boundary moved from left to right, and after continuously applying PD1–PD7, the cumulative displacement reached ~1170 nm; after switching to a −5 V negative trailing electric field (ND1–ND6), the vortex boundary moved back by ~928–1400 nm and gradually returned to its initial position. Moreover, merely changing the tip motion direction while keeping the polarity unchanged also enabled reversible reciprocating motion of the boundary. To verify this controlled process in real time at the atomic scale, the research team carried out experiments using a ZEPTOOLS transmission electron microscope in situ probe holder. By applying a +17 V electric field to the electrode through a tungsten tip, they observed in real time that the vortex cores reconstructed from a zigzag arrangement into a nearly flat configuration and formed a clear boundary. After removing the electric field, the vortex topological state remained stable, and subsequent application of the electric field again could move the boundary further to the right. These results are highly consistent with the PFM observations, strongly confirming that vortex boundary motion possesses a topologically protected nature.

The study then further revealed the microscopic physical mechanism of the controlled motion of vortex boundaries. Phase-field simulations based on the time-dependent Ginzburg–Landau equation show that the motion is dominated by switching of the zigzag pattern at the vortex core, and that the total energy profile exhibits a significant peak during boundary displacement, corresponding to the transient state in which the vortex configuration is distorted under the applied electric field; after relaxation, the energy drops to a new local minimum. The gradient energy (including Dzyaloshinskii–Moriya-type interactions) decreases when the electric field is applied because vortex rotation is partially suppressed, and then rises sharply after the field is removed as the vortices reconstruct. The energy peak originates from the transient antiparallel alignment between the local polarization and the external field. Reversing the polarity of the electric field can drive the boundary back to its original position and realize reversible motion. The boundary displacement under continuous bias in the simulations is consistent with the in situ experimental observations, fully clarifying from an energy perspective the physical origin of the reversible motion of vortex boundaries driven by a trailing electric field.

The study ultimately focused on the temporal stability of vortex boundary motion and its device application potential. After reproducing the experiment in a new region, the team carried out hourly evolution monitoring of the moved vortex boundary for as long as 120 days. The results showed that after 2 days, 8 days, 30 days, and 120 days, no measurable relaxation occurred in the moved vortex boundary, and the displacement state was retained over the long term. This is attributed to the intrinsic topological protection of the vortex structure, which suppresses spontaneous reversal, in sharp contrast to the behavior of conventional ferroelectric domains, which readily relax back to their initial configuration. The study also found that the application of a local electric field can not only drive vortex switching at the target site but also induce long-range nonlocal modifications spanning hundreds of nanometers, reflecting the inherent collective and nonlocal nature of order-parameter dynamics. This lays a solid foundation for the development of next-generation low-energy-consumption, high-density nanoelectronic devices such as ferroelectric racetrack memories, reconfigurable logic devices, and ultrasmall tunable capacitors and transistors.

As a high-end precision instrument company based in China, ZEPTOOLS is a first-class supplier of in situ electron microscopy characterization solutions. Its PicoFemto series of in situ transmission electron microscopy characterization solutions have successively provided technical support for important research results by users at home and abroad. The figure below shows the ZEPTOOLS in situ TEM sample holder product used in this research: