Electrons Drive a Molecular Archimedes Screw in University Collaboration
Scientists have built a molecular motor that spins when electrical current passes through it, adapting the ancient Archimedes screw design to the scale of a single molecule. The device can reverse its direction when the electrical voltage polarity is switched, marking a step toward functional machines at the atomic scale.
Researchers in Copenhagen, Israel, and Germany collaborated on the project. The central component is a spiral molecule created by the research group of Michael Pittelkow at the University of Copenhagen. Measuring a few millionths of a millimeter, the molecule binds to gold surfaces using sulfur atoms.
Gold Electrodes Stretch and Compress the Helix
At the Weizmann Institute of Science in Israel, a team led by Oren Tal and Anil Kumar Singh positioned individual spiral molecules between two gold tips sharpened to atomic dimensions. By adjusting the distance between these electrodes, the researchers stretched or compressed the molecular screw.
Applying an electrical voltage caused the molecule to rotate. Reversing the voltage’s polarity reversed the direction of rotation. Electrons traveling through the spiral structure transfer angular momentum, producing continuous rotation once the voltage exceeds a threshold.
Supercomputer Simulations Reveal a Hundredfold Electrical Effect
Experiments showed that the rotating molecule conducted electricity up to 100 times more efficiently than when it was stationary. To gain insight into this phenomenon, quantum mechanical calculations were run on the LiCCA supercomputer by Fabian Pauly alongside PhD students Léon Martin and Yuta Ito, all based at the Chair of Theoretical Physics I at the University of Augsburg.
The calculations revealed that conductivity changes by up to two orders of magnitude depending on the molecule’s angle. “The surprising thing is that it is precisely the positions that the molecule avoids when at rest that conduct electricity best. It is only the rotation that makes these positions accessible,” Léon Martin explained.
The researchers worked with theoretical physicists Per Hedegård of the Niels Bohr Institute and Jing-Tao Lü of Huazhong University of Science and Technology.
Future Applications
Collaborative Research Center (SFB) 1585 (project number 492723217) provided financial backing for the efforts at the University of Augsburg via the German Research Foundation (DFG). The computational research was conducted using the LiCCA supercomputer at the University of Augsburg. Financial backing for the partner institutions was additionally provided by the European Research Council (ERC, Horizon 2020, Grant 864008), the Israel Science Foundation (2129/23), the Minerva Foundation, the Villum Foundation, the Novo Nordisk Foundation, the Independent Research Fund Denmark (DFF), the National Key Research and Development Program of China, and the National Natural Science Foundation of China.
