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Topological Polar Textures in Freestanding Ultrathin Ferroelectric Oxides

Franco N. Di Rino, Tim Verhagen

TL;DR

This work addresses the rich topology of polarization in freestanding ultrathin ferroelectric oxides, using a first-principles-derived core-shell model to map how polarization textures in BaTiO$_3$ evolve with layer thickness $N_z$ and temperature. The authors perform large-scale molecular dynamics simulations in a freestanding geometry, varying lateral sizes and thicknesses, and analyze both real-space polarization patterns and their structure factors, including the response to time-dependent THz fields. They identify distinct low-temperature textures—wave-helix and chiral-bubble states with near-degenerate energies (difference ~ $0.3$ meV per formula unit)—and a higher-temperature vortex-labyrinthine regime with tetratic orientational correlations, transitioning to isotropic fluctuations as $T$ rises. Crucially, they demonstrate reversible switching between textures via static and time-dependent electric fields, suggesting a route to dynamically engineer topological states in nanoscale ferroelectrics and highlighting the potential of freestanding oxide layers as minimal platforms for topological ferroic phenomena. The results connect 2D material-inspired design principles to complex oxide physics, offering insights for future ferroic devices and nonlinear phononics-driven control of polarization textures.

Abstract

The remarkable advances achieved in two-dimensional materials are now being directly transposed to low-dimensional oxides. Here we show using first-principles-based atomistic simulations that ultrathin freestanding ferroelectric layers host a rich variety of polar states, from liquid-like ferroelectric domains with long-range orientational order to helix-wave and chiral bubbles configurations reminiscent of those observed in twisted freestanding oxide layers. Time-dependent electric fields enable reversible control, revealing freestanding oxide layers as ideal platforms to explore complex polar states and their potential applications in future ferroic devices.

Topological Polar Textures in Freestanding Ultrathin Ferroelectric Oxides

TL;DR

This work addresses the rich topology of polarization in freestanding ultrathin ferroelectric oxides, using a first-principles-derived core-shell model to map how polarization textures in BaTiO evolve with layer thickness and temperature. The authors perform large-scale molecular dynamics simulations in a freestanding geometry, varying lateral sizes and thicknesses, and analyze both real-space polarization patterns and their structure factors, including the response to time-dependent THz fields. They identify distinct low-temperature textures—wave-helix and chiral-bubble states with near-degenerate energies (difference ~ meV per formula unit)—and a higher-temperature vortex-labyrinthine regime with tetratic orientational correlations, transitioning to isotropic fluctuations as rises. Crucially, they demonstrate reversible switching between textures via static and time-dependent electric fields, suggesting a route to dynamically engineer topological states in nanoscale ferroelectrics and highlighting the potential of freestanding oxide layers as minimal platforms for topological ferroic phenomena. The results connect 2D material-inspired design principles to complex oxide physics, offering insights for future ferroic devices and nonlinear phononics-driven control of polarization textures.

Abstract

The remarkable advances achieved in two-dimensional materials are now being directly transposed to low-dimensional oxides. Here we show using first-principles-based atomistic simulations that ultrathin freestanding ferroelectric layers host a rich variety of polar states, from liquid-like ferroelectric domains with long-range orientational order to helix-wave and chiral bubbles configurations reminiscent of those observed in twisted freestanding oxide layers. Time-dependent electric fields enable reversible control, revealing freestanding oxide layers as ideal platforms to explore complex polar states and their potential applications in future ferroic devices.
Paper Structure (3 sections, 2 equations, 4 figures)

This paper contains 3 sections, 2 equations, 4 figures.

Table of Contents

  1. Acknowledgement
  2. End Matter
  3. Simulation method

Figures (4)

  • Figure 1: Ferroelectric phases diagram (layer thickness N$_z$ - temperature) in free standing BTO thin layers.
  • Figure 2: Representative three-dimensional polarization textures stabilized at different temperatures in a freestanding BTO layer ($N_z=12$). (a) Vortex labyrinthine structure vector field. Streamlines serve as a guide to the eye (405 K). (b) Wave-helix (7 K). Cross-sectional view along a $\langle110\rangle$ plane. Streamlines serve as a guide to eye. (c) Chiral-bubbles (7 K) vector field exhibiting square-like domain organization with alternating $P_z$ orientation.
  • Figure 3: Cross-sectional vector field view along a $\langle001\rangle$ plane.(a) Topological density charge $\mathrm{q}$ and (b) chirality density $\chi$ map.
  • Figure 4: Top-view snapshots of the out of plane polarization component ($P_z$) of the layer. Panels (a), (c), (e), and (g) show instantaneous configurations at 7 K (stripe domain), 7 K (chiral-bubble domain), 300 K, and 325 K, respectively. The color lobes correspond to contour regions with similar $P_z$ values. Panels (b), (d), (f), and (h) display the corresponding time averaged structure factors of the out-of-plane polarization component $S(P_z)$