Synthetic Molecular Motor Employs Archimedes Screw Geometry to Rotate via Electric Current

An international team of physicists has constructed a nanoscale motor from a single helical molecule that rotates when exposed to an electric current. The breakthrough, detailed in the journal Nature, demonstrates that continuous rotation unlocks hidden quantum channels, amplifying the molecule's electrical conductivity by up to a hundred times.[1][2]

The design draws direct inspiration from the Archimedes screw, an ancient engineering mechanism used to transport water uphill. Instead of moving water, the molecular version uses a helical structure to channel a flow of electrons, which in turn sets the entire molecule spinning.[2][3]

While molecular motors powered by electricity have existed since 2011, previous iterations were confined to surfaces and required the tip of a scanning tunneling microscope to drive their movement. This new design is the first current-driven molecular motor with a controllable rotation direction that is firmly attached to two metal electrodes.[3][4]

The achievement establishes a physical foundation for ultra-fast molecular computing, frictionless nanoscale sensors, and spintronic memory devices that operate at the absolute limits of miniaturization. By proving that mechanical motion at the single-molecule level can be directly controlled and wired into conventional electrodes, the research bridges a critical gap in nanotechnology.[1][3]

Wiring a single molecule

The motor's central component is a specially engineered helical organic molecule measuring just a few millionths of a millimeter in length. Synthesized by researchers at the University of Copenhagen, the molecule features sulfur atoms at both ends, allowing it to bind securely to gold surfaces.[3][4]

To test the mechanism, experimental physicists at the Weizmann Institute of Science in Israel suspended individual molecules between two atomically fine gold tips. Operating at temperatures near absolute zero, the team could precisely adjust the distance between the electrodes to stretch or compress the molecular screw.[1][3]

When the researchers applied an electrical voltage across the junction, they detected cyclical jumps in the current flowing through the molecule. These sequential jumps indicated that the molecule was rotating in a specific direction, driven entirely by the electrical energy passing through it.[1][5]

The direction of rotation proved to be unambiguous and strictly determined by the molecule's inherent chirality—whether it was synthesized with a right-handed or left-handed coil. Crucially, the researchers found they could reverse the motor's spin simply by changing the polarity of the applied voltage.[3][4]

The electric wind

The driving mechanism relies on the transfer of angular momentum from the electrons to the physical structure of the molecule. As electrons flow through the helical pathway, they act much like wind blowing against the blades of a turbine, pushing the molecule into motion.[2][3]

Above a specific voltage threshold, the molecule's movement transitions from discrete, sequential jumps into a state of continuous rotation. It is at this critical juncture that the researchers observed a drastic, nonlinear surge in the overall electrical current passing through the junction.[1][3]

"We have shown that an electric current can be used to generate a directed rotation and that this rotation, in turn, controls the current," explains Professor Fabian Pauly of the University of Augsburg, who led the theoretical modeling. "This is a new operating principle for machines at the very limits of miniaturisation."[3]

To understand why a spinning molecule conducts electricity significantly better than a stationary one, theoretical physicists conducted quantum mechanical simulations on the LiCCA supercomputer. The calculations revealed that the molecule's conductivity depends heavily on its angle of rotation.[3][4]

Rotation-enhanced conductance

At rest, the helical molecule naturally settles into positions that are energetically comfortable, but these specific orientations turn out to be poor electrical conductors. The continuous rotation forces the molecule to visit highly conductive regions in its rotational energy landscape that it would otherwise avoid.[1][3]

"The surprising thing is that it is precisely the positions that the molecule avoids when at rest that conduct electricity best," says Léon Martin, a doctoral researcher at the University of Augsburg. "It is only the rotation that makes these positions accessible."[3]

This phenomenon, termed rotation-enhanced conductance, effectively turns the molecule into a mechanical switch with no conventional moving parts. Because the moving part is the molecule itself, the device conducts up to two orders of magnitude better while in motion than when standing still.[1][3]

Theoretical partners at the Niels Bohr Institute and Huazhong University of Science and Technology developed a simplified model that successfully reproduced the experimentally observed current increase. The model confirmed that the current-induced forces drive an avalanche effect that boosts the overall conductance.[1][3]

Future nanoscale applications

"In the experiment, you only see the current," notes Yuta Ito, a doctoral student who contributed to the simulations. "Our calculations allow us to glimpse what is happening inside the nanocontact. It was only through close collaboration between experiment and theory across several countries that the mystery of the current increase could be solved."[3]

The ability to control rotation direction and harness rotation-enhanced conductance opens new pathways for molecular electronic components. Researchers anticipate that similar architectures could eventually be integrated into spintronics, where the spin of electrons is used to store and process information.[3][5]

Beyond computing, the molecular Archimedes screw offers a novel tool for researching physical processes and chemical reactions at the atomic scale. By providing a reliable method to convert electrical energy into directed mechanical motion, the discovery brings science one step closer to the complex molecular machinery found in living cells.[2][3]

The research team plans to explore how different molecular geometries and electrode materials might further optimize the motor's efficiency. As nanotechnology continues to advance, these current-driven molecular machines could become foundational building blocks for the next generation of ultra-compact devices.[1][3]