Nanoscale twisting of oxides offers new solutions for information storage

Researchers from the Luxembourg Institute of Science and Technology (LIST) have participated in a study that has successfully created a unique and artificial crystal structure by stacking single-crystal layers of ceramic oxides at varying angles to one another. The resulting new generation of synthetic materials could provide solutions to enhance the information storage density and the energy efficiency of future computing devices. The study, led by the Complutense University of Madrid (UCM), in collaboration with LIST and the Institute of Materials Science of Madrid (ICMM-CSIC), has been published in Nature.

Novel approach to material creation

In natural or laboratory-grown crystals, atoms arrange periodically, forming layers stacked atop each other. These layers naturally grow facets and follow specific growth directions. “What sets this work apart is the ability to rotate one layer relative to the other, a process not observed in nature,” says Hugo Aramberri, Research and Technology (R&T) Associate within the materials department at LIST and one of the coauthors of the study. He says that by precisely controlling this rotation angle in the laboratory new properties emerge at the interface between the layers. These emergent properties differ from those found in individual layers.

The material under study here belongs to a category known as ferroelectrics - a type of substance that shows a spontaneous electrical polarization. Ferroelectric materials are similar to magnets in that they have positive and negative poles of electric charge instead of magnetic poles. And as is the case in magnets, these materials feature dipoles throughout. “Applying an electric field can reverse the polarity of these dipoles,” explains Aramberri. “This property holds promise for technological applications, as the orientation of these dipoles can encode information.” However, conventional ferroelectric materials lack precise control over individual dipoles, which restricts their ability to shrink memory storage down to the atomic level.

This research has led to the creation of oxide crystals with a new degree of freedom and atomic control non-existent in nature, exploring the novel concept of 'twistronics'. This technique involves deliberately rotating atomic-scale layers of crystals. Through the manipulation of these layers, unique motifs known as moiré patterns are created, influencing how the layers interact. According to theoretical models by Hugo Aramberri and Jorge Íñiguez-González, Lead R&T Associate at LIST and another coauthor of the study, these patterns are responsible for the emergence of new behaviours observed in the material. This interplay also leads to the formation of a ferroelectric state characterized by small vortices, or tiny whirlpools, of electrical polarization.

Significant potential for information storage and other implications

“Novel ways to manipulate individual dipoles at the atomic scale as in this case could enable new and more compact memory storage technologies,” says Aramberri. The research predicts storage densities exceeding 100 terabits per square inch, a significant leap beyond the current limit of 1 terabyte per square inch. This advancement is crucial for meeting the growing need for high-capacity, energy-efficient data storage, with the potential to surpass yottabytes within the next ten years.

As for further research, Aramberri says that while specific projects are not yet finalized, the study's broader implications include opportunities to explore and utilize new effects and characteristics in various crystalline oxides and other materials and investigating potential interactions with magnetism. “Ultimately, the goal is to leverage these insights to advance memory technologies, potentially achieving significantly denser information storage. While concrete plans are still in development, this research lays the groundwork for future discoveries,” he concludes.