A helical molecule strung between two gold tips rotates when current flows through it, and conducts up to a hundred times better in positions it cannot reach while standing still.

Archimedes’ screw moves water uphill by rotating a helix inside a cylinder. It is among the oldest machines still in use, and the principle is simple enough that it survives being shrunk — though not usually this far.

An international team led from the University of Augsburg reports in Nature a version built from a single molecule, a few millionths of a millimetre long, strung between two atomically fine gold tips and set turning by an electric current.

“We have shown that an electric current can be used to generate a directed rotation,” said Professor Dr Fabian Pauly, who holds the Chair of Theoretical Physics I at Augsburg. “This is a new operating principle for machines at the very limits of miniaturisation.”

Electrons as wind

The driving mechanism is angular momentum transfer. Electrons passing through the helical molecule hand some of their rotational momentum to it, which the team compares to wind driving a turbine.

Which way it turns is set by the molecule’s own geometry — the handedness of its coil — and can be reversed by flipping the voltage polarity. Above a certain voltage the motion stops being a jitter and becomes continuous rotation.

Molecular motors powered by current have existed since 2011, and the broader field of molecular machines was recognised by the 2016 Nobel Prize in Chemistry. What the team claims as new is a current-driven motor with controllable rotation direction bound between two metal electrodes — a configuration that matters because electrodes are how such a device would ever be wired into anything.

The result that was not expected

The more interesting finding is electrical rather than mechanical. The molecule’s conductance depends strongly on its rotation angle, and during rotation it can rise by up to two orders of magnitude.

The reason is a matter of which orientations the molecule visits. At rest it settles into positions that are energetically comfortable, and those turn out to be poor conductors. The best-conducting orientations are ones it avoids when standing still.

“It is only the rotation that makes these positions accessible,” said Léon Martin, a PhD student at Augsburg.

The consequence is a sharp, nonlinear jump: once rotation reaches a certain speed, the current increases abruptly by up to a hundredfold. A device that conducts a hundred times better while in motion than at rest is, in effect, a switch whose state is mechanical — and one with no moving parts in the conventional sense, because the moving part is the molecule itself.

Seeing what cannot be seen

Nothing in this experiment is directly observable. A single molecule between two gold tips produces one measurable output, and everything else has to be inferred.

“In the experiment, you only see the current,” said Yuta Ito, a PhD student at Augsburg. “Our calculations allow us to glimpse what is happening inside the nanocontact.”

That is the methodological heart of the work and its main vulnerability. The rotation is not watched; it is deduced from a current trace that matches what a rotating molecule would produce. A simplified theoretical model built by the team’s collaborators reproduced both the rotation and the current increase, which is the evidence that the interpretation is right — and it remains an interpretation rather than an image.

Ito credits the arrangement rather than either half of it: it was only through close collaboration between experiment and theory, he said, that the behaviour could be understood.

A long list of institutions

The division of labour is worth setting out, because it explains how a result like this gets assembled.

The molecule was created by the team of Professor Michael Pittelkow at the University of Copenhagen. The experiments were done by Professor Oren Tal and Dr Anil Kumar Singh at the Weizmann Institute of Science in Israel. The theoretical work came from Augsburg with Per Hedegård at the Niels Bohr Institute in Copenhagen and Jing-Tao Lü at Huazhong University of Science and Technology in Wuhan.

Synthesising a molecule with a specific helical handedness, measuring single-molecule conductance between gold tips held apart by atomic distances, and modelling current-driven mechanics are three different specialisms, and none of the three groups could have produced the result alone.

What it is not yet

The release does not report how fast the molecule turns, how much torque it produces, how long a given molecule survives being driven, or what fraction of attempts yield a working contact — and that last number tends to be the sobering one in single-molecule electronics, where contacts form and break unpredictably and measurements are statistical across many junctions.

Nor is there an application. A single-molecule rotor between gold electrodes is a demonstration of a principle, not a component, and the gap between the two in this field has historically been measured in decades. The 2016 Nobel recognised molecular machines partly on the understanding that their uses were still hypothetical, and that has not changed much.

What has changed is the control. A rotation whose direction is set by molecular handedness and reversible by voltage, producing a hundredfold conductance change as a side effect, is a more tractable object than the molecular motors that preceded it — and the conductance effect in particular is the kind of thing that finds a use before the motor does.

The work was funded by the German Research Foundation through Collaborative Research Centre 1585 (project 492723217) and the LiCCA supercomputer project (499211671), the European Research Council under 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, the National Key Research and Development Programme of China and the National Natural Science Foundation of China.

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Notes

1. “Current-Driven Molecular Machine with Rotation-Enhanced Conductance.” Nature, 2026. DOI: 10.1038/s41586-026-11312-x.
2. University of Augsburg. “Archimedes’ screw made from a single molecule.” EurekAlert!, 22 October 2026. https://www.eurekalert.org/news-releases/1148951.