Physicists from University of Jyväskylä and Aalto University (Finland) has realized experimentally a two-dimensional topological crystalline insulator. This is a quantum material that has been theoretically predicted for more than a decade but had remained inaccessible due to materials challenges.

Researchers realized long-sought two-dimensional topological material. The work was led by Associate Professor Kezilbeiek Shawulienu and carried out in collaboration with colleagues from Aalto University, including Professor Peter Liljeroth and Professor Jose Lado. The research team created the material by growing an atomically thin, two-layer film of tin telluride (SnTe) on a niobium diselenide (NbSe₂) substrate.

Using molecular beam epitaxy and low-temperature scanning tunneling microscopy, the researchers characterized the electronic properties of the system with atomic-scale precision. In this two-dimensional system, they observed pairs of conducting edge states, hallmarks of topological crystalline insulators, that are protected by the symmetry of the crystal lattice.

Strain as a key to controlling topological edge states

The edge states form within a large electronic band gap exceeding 0.2 eV. Measurements show that the SnTe film experiences compressive strain from the underlying substrate, which plays a crucial role in stabilizing the topological phase. Importantly, the results show that the topological edge states can be tuned by strain, providing a pathway to control their electronic properties.

Toward nanoscale devices

First-principles quantum-mechanical calculations confirm the topological origin of the observed edge states. The researchers also directly probed interactions between neighboring edge states, revealing energy shifts driven by a combination of electrostatic interactions and quantum tunneling. Because of the large band gap, the topological properties are expected to remain robust up to room temperature.

The results provide a new experimental platform for studying strain-tunable two-dimensional topological states and may enable future advances in spin-based electronics and nanoscale devices.

The results were published in the Nature Communications.