Ancient Water Pump Inspires Molecular Motor That Multiplies Electrical Current 100-Fold

A 2,000-Year-Old Idea, Reimagined at the Atomic Scale

Invented more than two millennia ago, the Archimedes screw is a giant corkscrew of sorts, with a spiral blade that rotates around its axis to pump water. Engineers have relied on its elegant simplicity ever since. But now, a team of international physicists has taken that ancient principle somewhere no one has gone before — down to the scale of a single molecule — and the results are stunning.

Researchers at the Weizmann Institute of Science and their colleagues created a molecular version of the famous screw and discovered a surprising relationship between electric current and rotational motion: when the current causes the molecule to rotate, the rotation, in turn, can enhance electrical conduction. The findings were published in the journal Nature and represent a genuine leap forward in the science of molecular machines.

How the Molecular Screw Works

In the study, researchers from the lab of Prof. Oren Tal of Weizmann's Chemical and Biological Physics Department suspended a single helical organic molecule between two gold electrodes at a temperature close to absolute zero. The movement is driven by the electrons themselves — as they flow through the helical molecule, they transfer angular momentum to it, much like the wind drives a wind turbine. The direction is determined by the molecule's coil, just as with a screw with a right- or left-hand thread.

When they applied a voltage between the electrodes, they detected cyclical jumps in the current flowing through the molecule; the sequence of the jumps indicated rotation in one direction. When the scientists reversed the direction of the current, the sequence of jumps was also reversed, indicating that the molecule was rotating in the opposite direction. This level of precision and control at such a tiny scale is exactly what scientists have been chasing for decades.

The biggest surprise came when they increased the voltage: above a certain threshold, the current flowing through the molecule surged by up to a hundredfold. According to the researchers' calculations, this sharp increase occurs when the molecule goes from sequential rotational jumps to continuous rotation, allowing electrons to pass through it more easily.

The Counterintuitive Physics Behind the Leap

As researcher Léon Martin explains, "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." In other words, the molecule is a better conductor when it's spinning than when it's sitting still — a deeply counterintuitive result that required quantum mechanical simulations on a supercomputer to fully explain.

Researchers also discovered that the threshold at which the current starts to increase sharply can be controlled by stretching or compressing the molecule, much like changing the angle of the blades in a turbine. The researchers can stretch or compress the molecular screw by adjusting the distance between the gold electrodes, giving scientists a practical dial for tuning the device's behavior.

Why This Discovery Matters

Molecular machines are regarded as the next step in miniaturization. Their models can be found in living cells, where molecular motors convert energy and generate movement — and scientists have been working for decades to artificially replicate such systems. The field gained international recognition with the 2016 Nobel Prize in Chemistry, awarded for the design and synthesis of molecular machines.

This discovery establishes a new way to couple mechanical motion and electricity at the smallest scales, opening new possibilities for molecular electronics. The new findings could inform future research into molecular electronics, spintronics, and microfluidic systems. Spintronics — technology that exploits the spin of electrons rather than just their charge — is considered one of the most promising frontiers for next-generation computing and data storage. A molecular motor that can control both rotation direction and conductivity with such precision could one day be a foundational building block for devices we can barely imagine today.