A molecule no wider than a few atoms has been made to spin on command, using nothing but an electric current.
An international research team led in part by faculty at the Indian Institute of Technology Madras has demonstrated that a single spiral-shaped molecule, held between two gold electrodes, can be driven through a repeating cycle of movements by an applied voltage — and that once it begins to rotate freely, its ability to carry current jumps by as much as a hundred times.
The findings, published in the journal Nature, offer a new window into how motion and electricity interact at the atomic scale, and point toward a future class of nanoscale components whose electrical behaviour can be controlled through movement itself.
The work brings together researchers from five countries — India, Israel, Germany, Denmark and China — combining laboratory experiments, molecular synthesis, theoretical modelling and quantum-mechanical calculations. The principal experimental contributor and corresponding author is Dr Anil Kumar Singh, Assistant Professor in the Department of Physics at IIT Madras, who leads work at the institute's Atomic-Scale Quantum Devices Laboratory.
The collaboration reflects how modern nanoscience now operates: no single laboratory can easily master the synthesis of an exotic molecule, the construction of a junction a single molecule wide, and the mathematics needed to explain what happens inside it, all at once.
At the heart of the experiment is a helicene, a molecule shaped like a tiny spiral staircase. The researchers suspended one such molecule between two gold electrodes, forming a junction so small that electrons must pass through the molecule itself to get from one side to the other. Such single-molecule junctions have been studied for years as possible building blocks of future electronics, but they are notoriously difficult to control.
A molecule in a junction can adopt many orientations, and each orientation conducts electricity differently. Until now, the relationship between a molecule's movement and the current flowing through it has been poorly understood — a gap that has limited the design of devices built from individual molecules.
When the team applied a voltage across the junction, something remarkable happened. The molecule did not sit still, nor did it move randomly. Instead, it moved through a cyclic sequence of configurations, stepping from one arrangement to the next in a fixed order.
In every one of the 122 cases in which the direction of the transition could be determined, the same sequence was observed — a striking consistency that rules out chance. Even more tellingly, reversing the polarity of the applied voltage reversed the sequence, running the molecular motion backwards. The motion was not merely a side effect of the current; it was electrically controlled, directed by the very voltage that drove electrons through the junction.
The real surprise came when the voltage was pushed beyond a certain threshold. At that point, the current through the junction rose sharply. The molecule, the researchers found, had shifted from its stepwise, preferred-orientation movement into continuous rotation, sweeping through configurations that allowed electrons to flow far more easily.
The result was an increase in electrical conduction of up to a hundred times. It was as though a stiff, reluctant hinge had suddenly become a freely spinning wheel, opening a much wider path for the current. The threshold at which this change occurred was not fixed: by stretching or compressing the junction, the team could adjust it, giving them a mechanical handle on an electrical property.
What the experiment reveals is a feedback mechanism operating at the atomic scale, in which molecular motion and electrical transport influence each other. The current drives the molecule to move, and the movement in turn changes how easily the current flows.
This two-way coupling is precisely what engineers would need to build molecular switches — components that flip between conducting and non-conducting states — and other nanoscale devices whose electrical properties can be tuned by movement rather than by simply switching a voltage on or off. In conventional electronics, a transistor controls current by an external gate voltage; here, the molecule's own motion becomes part of the control mechanism.
The result also speaks to a much older scientific dream: the molecular machine. Molecular machines are structures that perform a function in response to a stimulus — light, a chemical signal, or electricity. Nature uses them everywhere; the machinery inside living cells that copies genetic information, transports cargo and generates energy is built from molecular machines perfected over billions of years of evolution.
Chemists have learned to build artificial versions, and the field was recognised with the Nobel Prize in Chemistry in 2016. But a persistent challenge has been understanding, in detail, how an electric current can drive controlled motion in a single molecule, and how that motion then feeds back into the current. The new work answers both questions in a single experiment, at the level of one molecule.
The broader significance lies in the direction it opens for nanoelectronics. As conventional silicon transistors approach physical limits, researchers have long looked to single molecules as the ultimate miniaturised components. A molecule is, after all, the smallest possible building block of a device.
But harnessing molecules requires understanding them not as static wires but as dynamic objects that twist, flex and rotate — and that respond to the very currents they carry. The IIT Madras-led experiment shows that this dynamism is not a nuisance to be suppressed but a property to be exploited. A component whose conductance can be tuned a hundredfold by its own rotation is a fundamentally new kind of electrical element.
Dr Singh has been careful to temper excitement with realism. The demonstration is a fundamental proof of principle, not a technology ready for practical use. The experiments were carried out at cryogenic temperatures — 4.2 kelvin, about minus 269 degrees Celsius — conditions far removed from everyday electronics.
Making such a device work reliably at room temperature, and integrating single molecules into manufacturable circuits, will require substantial further research. The value of the work lies not in an immediate product but in establishing a physical principle: that electric current can drive controlled rotation of a single molecule, and that rotation can dramatically reshape its electrical behaviour.
That principle now gives researchers a concrete platform to build on. Future work will need to explore molecules that rotate at higher temperatures, junctions that survive repeated operation, and ways to read and control molecular motion in devices that can be fabricated at scale. Each of those steps is formidable, but each now has a clearer target, because the underlying physics has been demonstrated rather than merely predicted.
The study also showcases the strength of the international collaboration behind it, and the growing role of Indian institutions in frontier nanoscience, with IIT Madras contributing the central experimental work.
For now, the spinning helicene stands as a striking demonstration of control at the smallest possible scale: a single molecule, caught between two gold tips, turning in step with the current that flows through it, and in turning, opening the way for a hundred times more current to pass.
It is a reminder that at the atomic scale, the familiar boundaries between mechanics and electronics dissolve — and that the machines of the future may be built not from silicon, but from molecules in motion.
(Reporting based on Deccan Chronicle, ETV Bharat and Careers360.)