Twistronics is a research field that explores how stacking atomically thin layers with a slight twist between them can modify their physical properties. By controlling this twist, researchers can create new electronic and magnetic properties that are not present in the individual layers. A new study published in Nature Materials and led by researchers at ICN2 provides a remarkable example of this potential: the team used twistronics to generate polarisation vortices in a metallic material.

The researchers worked with ultra-thin membranes of strontium ruthenate (SrRuO₃), an oxide that is both electrically conductive and ferromagnetic. Their results show that polarisation vortices, a feature previously observed in insulating materials such as ferroelectrics, can also be achieved in metals. The key to achieving these polar textures is using torsional strain gradients in twisted bilayers of the metallic material. The paper reports that the polar vortices coexist with ferromagnetic ordering in the material, resulting in a “multiferroic metal”.

Properties that seemed incompatible

The relevance of the work is that it brings polar vortices and the larger area of “polar topology” into an enormous class of materials (metals) that had previously been thought to be incompatible with such entities. “Polar topology” here means the ability of electric dipoles (which are like the north and south poles of a battery, but at the atomic scale) to arrange themselves in sophisticated and rather robust nano-structures that can look like twists or knots. This robustness makes them promising candidates for potential applications in next-generation memory devices.

In metals, such tiny polar arrangements are hard to detect. In this study, the researchers used advanced electron microscopy to visualise them at the atomic scale. However, the vortices also have measurable consequences at a larger scale, because they affect the magnetisation and electrical resistance of the bilayers, which are easier to measure. The researchers expect that other functional properties, including optical and spintronic properties, may eventually also be shown to be sensitive to the presence of these vortices.

The research has involved advanced materials science to make twisted stacks of ultra-thin films (about 15 nanometres each) of this crystalline material, which were made by Dr Yingzhuo Lun and Dr David Pesquera at the Laboratory of Oxide Nanophysics, led by ICREA Prof. Gustau Catalan. The team also used cutting-edge transmission electron microscopy techniques, such as multislice electron ptychography, to visualise the atomic-scale polar vortices in 3D, with Xinxin Hu carrying out this work in the Advanced Electron Nanoscopy Group led by ICREA Prof. Jordi Arbiol.

These results were complemented by electronic property measurements done by Dr Yingzhuo Lun and first-principles theoretical modelling done by Dr Qi Ren and her colleagues in the group of Prof. Jiawang Hong at the Beijing Institute of Technology.

This is not the first time that ICN2 researchers have observed topological polar structures in unexpected materials. In 2025, they reported electric vortices and antivortices in PbZrO₃, an antiferroelectric material where the dipoles are normally antiparallel but can re-arrange themselves into such exciting structures. The new study takes this research a step further, showing that polarisation vortices can also emerge in a metal that has no dipoles at all in its initial non-twisted state, so the dipoles are both created and arranged in vortices through twistronics.

Read the open-access paper here: https://rdcu.be/PHBSg66gP7Za

Reference article:

Lun, Y.; Hu, X.; Ren, Q.; Saeed, U.; Gupta, K.; Mundet, B.; Pinto-Huguet, I.; Santiso, J.; Padilla-Pantoja, J.; Caicedo Roque, J. M.; Børstad Eriksen, M.; Merino, G.; Ma, Y.; Li, Q.; Zhu, B.; Tang, G.; Pesquera, D.; Wang, X.; Hong, J.; Arbiol, J.; Catalan, G. Polarization vortices in a ferromagnetic metal via twistronics. Nature Materials (2026). DOI:10.1038/s41563-026-02755-8.