Jun 19, 2024 
Discovery of onedimensional topological insulator
(Nanowerk News) A joint research team has unveiled a new topological insulator (TI), a unique state of matter that differs from conventional metals, insulators, and semiconductors. Unlike most known TIs, which are either threeor twodimensional, this TI is onedimensional. The breakthrough will lead to further developments of qubits and highly efficient solar cells.

Details of the research were published in the journal Nature ("Observation of edge states derived from topological helix chains").

TIs boast an interior that behaves as an electrical insulator, meaning electrons cannot easily move; Whereas its surface acts as an electrical conductor, with the electrons able to move along the surface.

Ever since threedimensional TIs were reported on in the 2000s, researchers have been on the hunt for new ones. Yet onedimensional TIs have remained largely elusive.


(a) Schematic of Te crystal which is formed by hexagonal arrangement of Te helix chains. (b) Single Te helix chain with boundary charge. (Image: Tohoku University)

"Onedimensional TIs are particularly intriguing because the electric charges that appear on their end points effectively constitute qubits  the basic unit of information in quantum computing. And hence vitally important to quantum physics," points out Kosuke Nakayama, an assistant professor at Tohoku University's Graduate School of Science and coauthor of the study.

Nakayama and his colleagues focused their attention on tellurium (Te), a semiconductor whose primary commercial use is in solar panels and thermoelectric devices. Recent theoretical predictions have suggested that single helix chains could in fact be onedimensional TIs. To verify this, the team needed to observe the electrical charges confined to the endpoints of these chains.

This required preparing clean edges of the Te chains without structural damage, something made possible by employing a newly developed gascluster ionbeam (GCIB) system, which can modify surfaces to within a nanometer. They then visualized the spatial distribution of electric charges using an angleresolved photoemission spectroscopy (ARPES) with a microfocused beam. Their investigations confirmed that the electric charges did indeed appear at the endpoints of the chains, thus supporting the onedimensional TI nature of Te.


Schematics of (a) threedimensional, (b) twodimensional, and (c) onedimensional topological insulators. (Image: Tohoku University)

Nakayama stressed that their research marks a crucial step toward understanding the properties of onedimensional TIs and will have wideranging benefits. "The charges at the endpoints of onedimensional TIs have a variety of uses: qubits, highefficiency solar cells, highsensitivity photodetectors, and nanotransistors. Our discovery of a onedimensional TI will help accelerate research towards the realization of these applications."

Besides Tohoku University, the team featured researchers from Osaka University, Kyoto Sangyo University, the High Energy Accelerator Research Organization (KEK), and the National Institute of Quantum Science and Technology.
