Dr. Esra van ’t Westende of the University of Twente, working in collaboration with researchers at Utrecht University, has led a study showing that quantum states in ultranarrow germanene nanoribbons can be switched on and off using only an electric field. The team focused on the topological end states that form in these atomically thin ribbons and demonstrated how precise adjustments to a local electric field allow those states to appear or vanish on demand. This behaviour, observed at the nanoscale, offers a practical route for controlling quantum states in solid-state materials without relying on complex architectures or magnetic fields.
Eek, L., van ’t Westende, E. D., Klaassen, D. J., Zandvliet, H. J. W., Bampoulis, P., & Smith, C. M. (2025). Electric-Field Control of Zero-Dimensional Topological States in Ultranarrow Germanene Nanoribbons. Physical Review Letters, 135(20), 206601. https://doi.org/10.1103/jx2x-fb5b
Germanene belongs to the same family of atomically thin materials as graphene, though it consists of germanium atoms arranged in a buckled honeycomb structure. In nanoribbons two to four hexagons wide, confined electronic modes appear at the ribbon ends. These modes are considered promising candidates for quantum computing because their topological character makes them less sensitive to environmental noise. The challenge has been to find a direct way to control them without relying on complex device architectures or magnetic fields.
The Twente and Utrecht team used a scanning tunneling microscope not only as an imaging tool but also as a method for creating a highly localized electric field above the nanoribbon. By adjusting the tip-to-sample distance, they varied the field strength and observed how the end states strengthened or faded. At lower field strengths, the narrow ribbons show a clear signature of the localized end state. As the electric field increases, this signal disappears entirely. In wider ribbons, the behaviour reverses: end states only emerge once the electric field exceeds a critical value.
Dr. Esra van ’t Westende of the University of Twente stated,
“By changing the distance between the scanning tunneling microscope and the nanoribbon, we adjust the local electric field. This allows us to literally switch the quantum state on or off.”
The experimental findings were supported by theoretical modelling carried out at Utrecht University. The calculations explain why ribbon width determines whether the electric field suppresses or activates the topological state. The models also show that the boundary conditions created by the buckled germanene structure are sensitive to field-driven changes in the electronic potential, providing a mechanism that aligns well with the measurements.
The research fits into a broader interest in materials that can host noise-resistant quantum states without heavy shielding or ultra-low temperatures. Earlier work in other two-dimensional materials has shown that structural confinement can yield localized quantum modes, but the ability to control these modes directly with an electric field gives germanene an additional level of tunability. This is important for device engineers, who prefer electrical control schemes because they can be integrated into scaled architectures more easily than magnetic or optical approaches.
The work is part of the Dutch national QuMat program, which links experimental and theoretical groups across institutions to accelerate quantum-materials development. The germanene study has been held up by program leaders as an example of how coordinated research efforts can translate fundamental materials physics into device-relevant insights.
While the demonstration is still at the laboratory stage, the results provide a clearer understanding of how engineered nanoribbons behave under local fields and highlight the role of atomic-scale design in future quantum hardware. If such systems can be stabilised and fabricated reproducibly, electrically switchable topological states may form the basis of more robust quantum bits or components within hybrid quantum architectures. For now, the work shows that the boundary between theory and experiment in quantum materials continues to narrow as techniques for probing and manipulating matter at the nanoscale improve.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
