The researchers hope that this vortex-like behavior of electrons in momentum space could form the basis for new quantum technologies such as orbitronics in the future. Here, the orbital torque of the electrons is used to transmit information in electronic components instead of the electrical charge. This could significantly reduce energy losses.
Momentum space versus local space
Momentum space is a physical concept that determines the movement of electrons based on their energy and direction of movement – and not on the specific location where they are located. Its “counterpart” is the so-called location space. This represents the environment in which everyday experiences such as water vortices or hurricanes are described. Even quantum vortices in materials have so far only been detected in local space: A few years ago, another ct.qmat team caused a worldwide sensation with the first three-dimensional image of a vortex-like magnetic field in the local space of a quantum material (Nature Nanotechnology 17 (2022) 250-255).
Theory confirmed
The fact that a quantum tornado is also possible in momentum space was predicted theoretically by Roderich Moessner eight years ago. The Dresden-based ct.qmat founding member published this quantum phenomenon back then as a “smoke ring”, because smoke rings also consist of vortices. Until now, however, it was unclear how these vortices could be measured at all. The experiments now showed that the quantum vortex is formed by so-called orbital angular momentum – i.e. the circular motion of the electrons around the atomic nuclei. “When we had the first indications that the predicted quantum vortices actually existed and could be measured, we contacted our Dresden colleague and started a joint project,” recalls Ünzelmann.
Quantum tornado found by extending a standard method
For the first detection of a quantum tornado in momentum space, the Würzburg research team further developed a special ARPES method (Angle Resolved Photo Emission Spectroscopy). “ARPES is part of the standard repertoire of experimental solid-state physics. It involves irradiating material samples with light, extracting electrons and measuring their energy and exit angle. This provides a direct view of the electronic material structure in momentum space,” says Ünzelmann. “If you make clever use of this method, you can measure the orbital angular momentum. I’ve been working on this since my dissertation.” ARPES is based on the photoelectric effect described by Albert Einstein, which is part of A-level physics knowledge.
In 2021, Ünzelmann had already expanded the method and attracted international attention with the detection of orbital monopoles in tantalum arsenide. The addition of a type of quantum tomography to ARPES has now made it possible to detect the quantum tornado – a new milestone. “We examined the sample layer by layer, as is known from medical tomography. The individual images were strung together. This allowed us to see the three-dimensional structure of the orbital angular momentum and prove that the electrons form vortices in momentum space,” explains Ünzelmann.
Würzburg-Dresden network cooperates worldwide
“The experimental proof of the quantum tornado is an example of the team spirit of ct.qmat. We successfully combine theory and experiment at the two physics locations of Würzburg and Dresden. In addition, experts work together with young scientists in our research network. This is a powerful driving force for research into topological quantum materials. In addition, almost every project in physics is the result of international cooperation – including this one,” comments Matthias Vojta, Professor of Theoretical Solid State Physics at TU Dresden and Dresden spokesperson for the Cluster of Excellence ct.qmat.
The tantalum arsenide material sample was grown in the USA and then studied at the international large-scale research facility PETRA III of the German Electron Synchrotron (DESY) in Hamburg. A scientist from China was also involved in the theoretical model creation, while a researcher from Norway led the experiment.
The ct.qmat team is currently investigating whether the material can be used to create orbitronic quantum components in the future.
Publication
T. Figgemeier, M. Ünzelmann, et al, “Imaging Orbital Vortex Lines in Three-Dimensional Momentum Space”, Physical Review X 15, 011032 (2025)
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.15.011032
Scientific contact
Dr. Maximilian Ünzelmann
Tel: 0931 31-86294
Email: maximilian.uenzelmann@uni-wuerzburg.de
About the Cluster of Excellence ct.qmat
The Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter has been jointly funded by Julius-Maximilians-Universität (JMU) Würzburg and Technische Universität (TU) Dresden since 2019. More than 300 scientists from over 30 countries and four continents are researching topological quantum materials that reveal surprising phenomena under extreme conditions such as ultra-low temperatures, high pressure or strong magnetic fields. The Cluster of Excellence is funded as part of the Excellence Strategy of the German federal and state governments – the only cluster in Germany that spans several federal states.
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Further links
👉 www.infineon.com
👉 www.infineon.com/risc-v
Photo: Jochen Thamm / think-design
