A research team at TU Ilmenau has discovered a previously unknown mechanism for optimizing and controlling the so-called Andreev reflection at the normal metal-superconductor interface. The findings may offer new opportunities in areas such as quantum computers or sustainable IT. The research results were obtained in collaboration with Aalto University in Finland and have just been published in the most important journal for physics research - Physical Review Letters - and were featured as "Editors' Suggestion" as well as specially highlighted in the Physics Magazine.
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Research at TU Ilmenau uncovers new mechanism for optimizing current across the normal metal-superconductor interface
Today, copper or aluminum are the standard materials for power lines in households, buildings or industrial plants. In these so-called normal conductors, electric current is transported by individual electrons. However, as these materials always have a certain electrical resistance, energy is lost in the form of heat when electricity is transported. Energy-intensive IT technologies are therefore increasingly relying on superconductors to transport electricity. Here, pairs of electrons, known as Cooper pairs, are transported without dissipation. As superconducting materials minimize electrical energy consumption, electronic circuits can work extremely fast - with several hundred billion switching operations per second.
Energy-efficient circuits and sustainable computers
In modern condensed-matter research, the interface between normal metals and superconductors has once again become the focus of increased interest. The reason: at this interface, electrons are converted into Cooper pairs and vice versa - a mechanism that was described in 1964 by the Russian physicist Alexander Andreev and is known as Andreev reflection. This process enables Cooper pairs to penetrate the normal metal - a phenomenon referred to as the superconducting proximity effect. "Hybrid structures made of semiconductors and superconductors, for example, are currently being intensively investigated due to the proximity effect, because they could be crucial components of future energy-efficient circuits, such as for sustainably operated computer architectures or IT technologies," explains Prof. Jörg Kröger, who is exploring Andreev reflection in the Experimental Physics I group together with his doctoral student Lorenz Meyer.
According to Lorenz Meyer, one particularly promising aspect is the possible use of the proximity effect in quantum computers, as the combination of magnetic nanostructures and conventional superconductors can create so-called Majorana quasiparticles - exotic particles that are considered key to particularly efficient and fault-tolerant quantum computers. According to the two scientists, such computers could massively lower the computing time of conventional digital computers in the long term.
Important step for "green electronics"
The team led by the physicists Lorenz Meyer and Jörg Kröger has now succeeded in controlling the Andreev reflection by external means. Using a scanning tunneling microscope operated at extremely low temperatures, a single molecule was used as a contact between a metal (tungsten) and a superconductor (lead). The special feature: The electronic properties of this molecule can be adjusted externally so that the effect is strengthened or weakened. These experimental results are reproduced by simulations carried out by a theory colleague at Aalto University in Finland, Professor Jose L. Lado. Prof. Kröger sees great potential in the research work of his team:
This discovery has great significance for the understanding of a quantum physical effect that was originally conceived for macroscopic interfaces, but has now been extended to contacts at the ultimate scale. Controlling the Andreev reflection at a quantum contact from the outside world could contribute to making superconducting effects usable in energy-efficient molecular electronics. This would be an important step forward for so-called "green electronics", which promises energy-efficient and sustainable technologies.
Publikation in Physical Review Letters
The research team's work was featured as an "Editors' Suggestion" by Physical Review Letters and as a highlight in the Physics Magazine. The project was supported by the German Research Foundation (DFG) and the Agence Nationale de la Recherche (ANR) as part of the project "Magnetic exchange interaction across a vacuum barrier on the atomic scale" (October 2024 - September 2027) and by the Federal Ministry of Education and Research (BMBF, ForLab project).
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M.Sc. Lorenz Meyer
Experimental Physics I Group