A research group at the University of Würzburg, in partnership with researchers from the University of Montpellier and the École Normale Supérieure in Paris, has recently created a topological insulator that demonstrates required characteristics even at elevated temperatures: around –213 °C, as experimental results have indicated. The study was published in the journal Science Advances.
A topological insulator can be thought of as a material that acts as a perfect insulator on the inside, it doesn’t conduct electricity through its interior. But along its edges or surfaces, it behaves quite differently, allowing electrons to move with minimal resistance. These boundary regions serve as nearly lossless “electron highways,” where electrons can travel efficiently with very little energy loss .
To expand on the analogy: these electron highways have designated lanes based on the electrons' "spin," a property related to their intrinsic angular momentum. Electrons with "spin-up" travel in one direction, while those with "spin-down" move in the opposite direction. This strict separation of traffic helps prevent scattering and collisions, significantly reducing energy loss. This behavior is known as the Quantum Spin Hall Effect (QSHE), a phenomenon first confirmed experimentally at the University of Würzburg .
A Quantum Well Structure with Three Layers
The primary benefit of this property is the potential for loss-free and spin-polarized electron transport, which may serve as the foundation for groundbreaking future electronic components. Despite the immense promise of this effect, its practical implementation has encountered significant obstacles thus far, primarily because topological insulators typically display their desired characteristics only at extremely low temperatures, just above absolute zero, approximately –273 °C.
This accomplishment was achieved by a team led by Professor Sven Höfling, Chair of Technical Physics, with Fabian Hartmann and Manuel Meyer serving as joint first authors.
We developed and tested a new material system for our experiments: a special quantum well structure consisting of three layers.
Sven Höfling, Professor and Chair, Technical Physics, University of Würzburg
Indium arsenide (InAs) constitutes the two outer layers of the three-layer configuration. The middle layer is composed of GaInSb, an alloy made from gallium (Ga), indium (In), and antimony (Sb). Physicists assert that this uniquely designed three-layer structure provides significant benefits compared to earlier methods.
A Promising Candidate for Technological Applications
“The problem with the materials used to date is often that their band-gap energy is too low,” said Fabian Hartmann.
The band gap can be conceptualized as a type of "energy barrier" that electrons need to surpass to render the material's interior conductive. Consequently, a larger band gap signifies a more substantial barrier, which inhibits the interior from achieving conductivity, even at elevated temperatures, thereby disrupting the loss-free edge channels.
Indeed, utilizing a GaInSb alloy enhances the band-gap energy of the material. Concurrently, incorporating a third InAs layer establishes a symmetrical structure that greatly enhances the magnitude and stability of the band-gap energy.
Our system is a promising candidate for technological applications because it combines three key advantages.
Manuel Meyer, Study Joint First Author, University of Würzburg
Firstly, it can be produced in substantial volumes and on a grand scale. Secondly, the outcomes are dependable and can be replicated. Lastly, the material is compatible with current silicon-chip technology.
In conclusion, the physicists are of the opinion that these findings lay the groundwork for the advancement of topological electronics. This could also function at more moderate temperatures and be effortlessly incorporated into existing semiconductor technology, thereby paving the way for a new era of energy-efficient and high-performance devices.
Journal Reference:
Meyer, M., et al. (2025) Quantum spin Hall effect in III-V semiconductors at elevated temperatures: Advancing topological electronics. Science Advances. doi.org/10.1126/sciadv.adz2408