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Rapid Test for Topological 2D Materials: A New Milestone

Researchers from the Würzburg-Dresden Cluster of Excellence ct.qmat have created a technique that makes it easier and faster to identify two-dimensional topological materials. The technique is featured as the lead article in the journal Physical Review Letters.

Quantum physicists at the Würzburg-Dresden Cluster of Excellence ct.qmat have developed a rapid test method to systematically identify topological 2D materials in record time. It uses special X-Rays to detect the different orbital angular momenta of electrons (shown in blue and red). The method was developed using the quantum material indenene, which has a triangular atomic structure. Image Credit: Christoph Mäder/Jörg Bandmann, pixelwg

Future technological breakthroughs are expected to be based on topological quantum materials. However, verifying their extraordinary attributes has always been a time-consuming task.

However, researchers from the Center of Excellence ct.qmat have created an experimental method that uses a quick test to consistently identify two-dimensional topological materials. This discovery could accelerate the development of this rapidly expanding class of materials.

Cutting-edge Research is Highly Complex and Time-consuming

In 2007, Professor Laurens W. Molenkamp, a pioneer of the Würzburg-Dresden Cluster of Excellence ct.qmat—Complexity and Topology in Quantum Matter, presented the first experimental demonstration of topological insulators. These materials are unique in that they conduct electrons on their surface without any resistance, despite the fact that their interiors act as electrical insulators.

Since that remarkable discovery, global interest in these minerals has grown significantly. This is due to their crucial role in the potential materials revolution and prospective applications in quantum technologies, such as the creation of “cold chips” that are powerful, energy-efficient, and do not emit waste heat.

Currently, detecting topological insulators experimentally entails highly complex research. It requires a large team and a substantial amount of time to prepare a sample of the material. Moreover, successful detection is never assured.

Prof. Dr. Ralph Claessen, Head of Chair, Universität Würzburg

Rapid Test for the Materials Revolution

However, a ct.qmat research team in Würzburg has developed a systematic approach for identifying two-dimensional topological quantum materials in record time using a simpler measurement methodology.

Essentially, in addition to a promising material sample, all you really need is special X-Rays. The required light particles should be high-frequency and circularly polarized, meaning they possess angular momentum. This can be achieved using any synchrotron light source. For instance, our samples were irradiated at the Elettra Sincrotrone in Trieste and at the Diamond Light Source, the UK’s national synchrotron science facility at the Harwell Science and Innovation Campus in Oxfordshire.

Dr. Simon Moser, Project Lead, University of Würzburg

What appears to be a simple concept is actually a huge development in the field of topological quantum materials.

Moser added, “If you secure a slot at a synchrotron, you can determine within about a week whether a material is a topological insulator. With the traditional method, this takes at least a doctoral thesis.

Spinning Success with Dichroic Photoemission

The essence of the new quick-testing approach is dichroic photoemission. The material sample is repeatedly subjected to high-frequency light with variable polarization. Initially, only electrons rotating clockwise, for example, are liberated from the material. As a result, only electrons rotating counterclockwise are emitted.

Detecting the various rotation directions of electrons via dichroic photoemission and, therefore, revealing their topology is not a novel concept. In 2023, another ct.qmat team from Würzburg utilized this approach for the first time to examine the topology of a kagome metal.

They used circular photoemission to investigate the kagome metal. We focused on the methodology and developed a kind of recipe that now always works, not just by chance. Our rapid test systematically makes the topology of the electrons visible,” Moser added.


The two-dimensional quantum material indenene, which the researchers have long studied, was also employed in the development of the quick test technique. They have also already extended the concept to different materials. A sample of bismuthene was exposed to radiation in a recent experiment; the results will be examined soon.

Journal Reference:

Erhardt, J., et al. (2024) Bias-Free Access to Orbital Angular Momentum in Two-Dimensional Quantum Materials. Physical Review Letters. doi:10.1103/PhysRevLett.132.196401.

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