Room-temperature polar skyrmions — nanoscale, topologically winding textures of the ferroelectric polarization first observed in 2019 in PbTiO3_3/SrTiO3_3 superlattices — were proposed as electrically controllable building blocks for high-density, low-power nanoelectronics, including electrically tunable negative capacitance. The open problem is to establish reproducible, deterministic control of these polar-skyrmion bubbles by applied electric fields: not only their creation, erasure and switching (now experimentally advanced), but above all their translation and mobility at device-relevant speeds and energy costs under realistic boundary conditions (electrode geometries, temperature cycles, defect landscapes); to quantify and harness experimentally the enhanced dielectric susceptibility and negative capacitance associated with the bubbles in practical device geometries; and to map the generality of polar-skyrmion stabilization across other ferroelectric material systems and epitaxial-strain regimes. As of 2026, field-driven creation/erasure/multistate switching has been demonstrated in several platforms; the only experimental skyrmion-relocation result is a pulse-induced 'teleportation' whose deterministic control its authors explicitly defer to future work; device-level negative-capacitance results remain simulation-only; and deterministic electric-field motion has been demonstrated experimentally only for adjacent topological objects (three-fold polar vertices, vortex boundaries). The deterministic-motion and harnessing core therefore remains open.

Background

A ferroelectric is a crystal whose local electric polarization (a vector order parameter) can point in discrete symmetry-related directions and be switched by an electric field; in an ultrathin ferroelectric film the interplay of exchange-like gradient energy, electrostatic (depolarizing) energy, and strain competes with the domain-wall energy and can stabilize swirling polarization textures instead of simple stripe domains. A polar skyrmion (or polar-skyrmion bubble) is such a nanoscale texture in which the polarization winds continuously, e.g. from up in the core, radially through the domain wall, to down outside, carrying an integer topological winding number (skyrmion number) that cannot be changed smoothly. Hong and Chen (2018) predicted by phase-field simulation (a mesoscale continuum method evolving polarization and field variables in time) that PbTiO3_3/SrTiO3_3 (PTO/STO) oxide superlattices should host stable 'polar-skyrmion bubbles' a few nanometers across. Das et al. (Nature, 2019) confirmed this experimentally: resonant soft X-ray diffraction (a synchrotron probe of nanoscale polarization periodicities) and its circular dichroism (the difference in scattering between left- and right-circularly polarized X-rays, which senses handedness), together with scanning transmission electron microscopy, showed skyrmion-number +1, Néel-like (radially oriented) bubble walls of roughly 8 nm periodicity, self-assembled into a polar-skyrmion lattice that is stable at room temperature without any external field. The paper further highlighted an enhanced local susceptibility of the bubble cores — a candidate for electrically controllable negative capacitance (a regime in which the differential capacitance of a ferroelectric element is effectively negative, allowing voltage amplification and lower switching energy in transistors) — and pointed to device applications if the bubbles could be electrically created, moved, and switched. The direct motivation is the magnetic analogue: magnetic skyrmions in metals can be driven by currents along 'racetrack' tracks toward nonvolatile memory, and the electric version promises the same nanoscale topological carriers without dissipative charge currents. Subsequent work established field-driven creation, erasure and reversible topological transitions of the bubbles (Zhu et al., in-situ biasing in a scanning transmission electron microscope, 2022; Zhou et al., phase-field local-electrode control, 2022), probe-based write/read of skyrmion arrays in metallic-contact PbTiO3_3 with densities beyond 300 Gbit/inch2^2 (Sun et al., 2025), multistate nonvolatile resistance switching of a single bubble in a van der Waals (layered, exfoliatable) ferroelectric, CuInP2_2S6_6, on silicon (Lan et al., 2026), and skyrmion lattices in further systems (bulk Bi0.5_{0.5}Na0.5_{0.5}TiO3_3, Yin et al. 2021; ferroelectric-metallic heterostructures, Sun et al. 2025). In parallel, theory has attacked the motion problem: phase-field simulations of motion under combined thermal, electrical and mechanical stimuli (Hu et al., 2023); atomistic simulations of field-gradient-driven bubble motion and 'teleportation' in ultrathin Pb(Zr0.4_{0.4}Ti0.6_{0.6})O3_3-based films, accompanied by a piezoresponse-force-microscopy experiment (a scanning-probe technique that images and locally perturbs ferroelectric domains through a conductive tip) in which a single voltage pulse nucleated a new bubble nanodomain while a neighboring bubble disappeared — an experimental demonstration of the feasibility of teleportation whose deterministic control the authors explicitly defer to future work (Prokhorenko et al., 2024); second-principles (intermediate-scale first-principles-derived) simulations of creep-limited (slow, thermally activated hopping over pinning barriers) displacement of domain textures under inhomogeneous fields (Gomez-Ortiz et al., 2025); and nudged-elastic-band quantification (a method that computes the minimum-energy path and its energy barrier between two configurations) of the skyrmion motion barrier (Hu et al., 2025). Deterministic, controlled electric-field motion has instead been demonstrated experimentally only for adjacent topological objects — isolated three-fold polar vertices (Li et al., 2022) and polar vortex boundaries steered by a conducting atomic-force-microscopy tip (Gupta et al., 2026) — and negative capacitance from field-driven skyrmions has so far been treated only theoretically (Guo et al., 2025). What has not been achieved is deterministic, reproducible, device-relevant control — translation in particular — of the polar-skyrmion bubbles themselves, together with experimental quantification of the skyrmion-associated susceptibility in practical device geometries and a map of the textures' stability across materials and strain regimes.

Problem Statement

Can room-temperature polar-skyrmion bubbles be deterministically and reproducibly controlled by applied electric fields to the standard required for device architectures? Concretely, for the nanoscale skyrmion-number +1 polarization textures first observed in PbTiO3_3/SrTiO3_3 superlattices and their analogues in other ferroelectric systems: (1) demonstrate reproducible electric-field-driven translation (motion, mobility) of individual polar-skyrmion bubbles — not only their creation, erasure and switching, which are now experimentally established — at device-relevant speeds and energy costs, under realistic boundary conditions including top-electrode geometries, temperature cycles and defect/pinning landscapes; (2) quantify experimentally the enhanced local susceptibility of the bubble textures and determine whether their electrically controllable negative capacitance can be harnessed in practical device geometries (e.g. as a voltage-amplifying element), rather than only predicted by simulation; (3) establish the operational stability, retention/lifetime, and the energetics of creation, annihilation and motion of these bubbles under those realistic conditions; and (4) determine the generality of polar-skyrmion stabilization across other material systems (bulk ferroelectrics, ferroelectric-metallic heterostructures, van der Waals ferroelectrics) and epitaxial-strain regimes. The four sub-goals share one objective — converting an observed equilibrium topological texture into an electrically programmable, device-usable state variable — which requires a reproducible field-control protocol (including translation) with quantified speed, energy cost and stability in at least one device-compatible geometry — an electrode-connected device stack, rather than an in-situ microscopy or scanning-probe setup — experimental quantification and harnessing of the skyrmion-associated enhanced susceptibility and negative capacitance in that device-compatible geometry, and a map of the materials and epitaxial-strain conditions for the validity of the stabilization and control across the material systems identified in (4).

References

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