Researchers from the University of Twente and Utrecht University created ultrathin nanoribbons made of germanium atoms that are only one atom thick. The researchers have demonstrated that this system has remarkable qualities that may be applied to quantum computing and more. The study was published in Nature Communications.
Image Credit: University of Twente
The dimensionality of quantum systems affects their characteristics. The properties of one-dimensional quantum systems differ from those of two-dimensional nanoribbons. Due to their special electronic characteristics, two-dimensional topological insulators are at the forefront of condensed-matter physics. Although they have insulating interiors, their edges are highly conductive, allowing electricity to flow freely.
Can We Go Smaller?
These unique properties make topological insulators promising materials for both quantum computing and the development of next-generation, energy-efficient electronic devices.
But as we try to make devices smaller and more efficient, there are key questions that remained unanswered. Like, what is the smallest size a topological material retains its two-dimensional properties? And what happens when we go smaller?
Pantelis Bampoulis, Study Researcher and Study Corresponding Author, Physics of Interfaces and Nanomaterials, University of Twente
To investigate these questions, the researchers utilized germanene nanoribbons, a material consisting of an atomically thin layer of germanium atoms known for its distinct topological characteristics.
Germanene Nanoribbons
In our work, we made germanene nanoribbons. These are structures that are just a few nanometers wide but hundreds of nanometers long. With germanene nanoribbons, we studied both theoretically and experimentally how the topological edge states change as the ribbons get narrower and narrower.
Dennis Klaassen, Ph.D Student and Study First Author, Physics of Interfaces and Nanomaterials, University of Twente
Klaassen was supervised by Bampoulis.
The study revealed that germanene nanoribbons retain their topological edge states down to a critical width of approximately 2 nm. Below this threshold, the typical edge states vanish, replaced by novel quantum states concentrated at the nanoribbon ends. These end states, safeguarded by fundamental symmetries, signify the formation of a one-dimensional topological insulator.
Possible Quantum Applications
These end states exhibit high stability against defects and impurities, making them ideal for quantum applications, such as the development of error-resistant qubits.
Interestingly, these states are similar to Majorana zero modes, which are elusive particles that have fascinated scientists ever since their prediction. Although we do not address Majorana zero modes, our study provides a template for exploring such phenomena in a one-dimensional material with strong spin-orbit coupling.
Pantelis Bampoulis, Study Researcher and Study Corresponding Author, Physics of Interfaces and Nanomaterials, University of Twente
“On top of that, the fabrication procedure allows us to make dense arrays of topological edge states where current could flow without dissipation, fulfilling a major requirement for low-energy electronics,” said Klaassen.
Journal Reference:
Klaassen, J. D., et al. (2025) Realization of a one-dimensional topological insulator in ultrathin germanene nanoribbons. Nature Communications. doi.org/10.1038/s41467-025-57147-4