Oral presentation

Session Information

Location: Science and Cultural Center - FORTH
Day: 3. Friday 18th
Time: 11:00-11:30
Chairperson: to be announced…

Presentation Details

Presentation Type: Oral presentation
Title: Arrays of Polar Helices at Twisted Bonded Ferroelectric Interfaces
Abstract: Recently, the field of Moire twistronics has expanded beyond 2D and Van der Walls materials to include oxides. By growing, detaching and stacking free-standing oxide layers with relative lattice twists, a host of novel structural and electronic phases have been stabilised. Perhaps the most interesting is the observation of non-trivial polarisation textures at the interfaces between these stacked layers. Arrays of polar vortices have been observed in twisted layers of ferroelectric [1], non-ferroelectric [2] and even metallic [3] oxides, and is typically related to the flexoelectric coupling between polarisation and the strain gradients that form. Herein, we describe an alternative approach to generate twisted ferroelectric interfaces and elucidate the emergent phenomena that we observe. By thermal annealing of single crystals of ferroelectric lithium niobate at high temperature, we can create covalently bonded interfaces with full control over twist angle, and the sense of ferroelectric bound charge at the interface (head-to head, positive or tail-to-tail, negative). We will show that enhanced conductivity emerges at the head-to-head interfaces, except at specific twist angles which correspond directly to a loss long-range lattice periodicity in the Moire pattern. Secondly, we will show that an array of structural helices emerges at these bonded interfaces, as revealed by plan-view DPC-STEM imaging. These structural helices imply a corresponding polar helix, based on direct piezoelectric coupling. The observed helices are slightly more complex than planar vortices: they should extend for certain depth away from the interface, and should exhibit a distinct chirality, embedded within the rotational sense of the helix. Indeed, circular dichroism SHG measurements confirm the interface hosts a clear chiral signal. Finally, we begin to explore the dynamics of these helices. Though structural in nature, tight binding modelling suggests that these helixes are dynamic and can be manipulated by the application of strain. These “twistrons” represent a complex interplay between structural chirality, polar topology and emergent conductivity, yet their emergence is governed by one simple parameter: twist. 1. Sánchez-Santolino, G. et al. A 2D ferroelectric vortex pattern in twisted BaTiO3 freestanding layers. Nature 626, 529–534 (2024). 2. Sha, H. et al. Polar vortex hidden in twisted bilayers of paraelectric SrTiO3. Nat Commun 15, 10915 (2024). 3. Lun, Y. et al. Polarization Vortices in a Ferromagnetic Metal via Twistronics. Preprint at https://doi.org/10.48550/arXiv.2505.17742 (2025).

Presenter

Dr Conor McCluskey
Queen's University Belfast | United Kingdom

Authors

1. McCluskey, Conor J. | School of Mathematics and Physics. Queen's University Belfast, UK
2. Holsgrove, Kristina | School of Mathematics and Physics. Queen's University Belfast, UK
3. Lynch, Ronan | {Affiliation3:value}
4. Todorov, Tchavdar | School of Mathematics and Physics. Queen's University Belfast, UK
5. Kumar, Amit | School of Mathematics and Physics. Queen's University Belfast, UK
6. McQuaid, Raymond | School of Mathematics and Physics. Queen's University Belfast, UK
7. Cherifi-Hertel, Salia | Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, France
 8. Koppitz, Boris | Institute of Applied Physics, TU Dresden, Germany
 9. Eng, Lukas | Institute of Applied Physics, TU Dresden, Germany
 10. Gregg, J. Marty | School of Mathematics and Physics. Queen's University Belfast, UK