A Rail System Built From Single Atoms Could Make Superconductors Leak Less Energy

Physicists in Japan have shown that steps in a crystal surface only one atom high can act as rails that steer the flow of quantum vortices through an ultrathin superconductor, a finding that could point toward superconducting circuits that waste far less energy than today's chips. The result, from a team at the International Center for Materials Nanoarchitectonics (MANA) at Japan's National Institute for Materials Science, was published in the journal Physical Review B over the summer and detailed in a research highlight posted by the institute in late September; it has since been circulating through science-media channels, reaching wire aggregator ScienceDaily's science digest this week.

In a superconductor exposed to a magnetic field, the field does not stay out entirely. Instead it penetrates in discrete bundles called vortices, each one a tiny whirlpool of circulating current with a non-superconducting core at its center. Where those vortices go, and how easily, determines how much energy a superconducting device loses when it operates — a problem that has limited practical use of superconducting electronics for decades. The MANA team's experiment shows that a far simpler structural trick than anyone had engineered before can almost fully control that motion.

A thousand-fold difference, one atomic step at a time

The researchers worked with an atomically thin superconducting layer of indium grown on a silicon crystal — a well-studied system known to specialists as Si(111)-(√7×√3)-In. By cutting the silicon wafer at a slight angle before growing the indium layer, they produced a "vicinal" surface covered in regularly spaced steps, each about 0.31 nanometers high, which is the height of a single atomic layer. The flat terraces between steps averaged roughly 89 nanometers wide, a figure that matters because it sits close to the 80-to-100-nanometer width of the vortex cores that form in this particular material.

Using a scanning tunneling microscope cooled to 0.4 kelvin, just a fraction of a degree above absolute zero, the team imaged the steps directly and located individual vortices sitting along them. They then wired the sample with two separate four-terminal electrode configurations, letting them push vortices with a Lorentz force either along the steps or across them, and measured the resulting electrical resistance in each direction. At intermediate magnetic fields, vortices moved more than 1,000 times more easily along the atomic steps than across them. Between roughly 0.10 and 0.20 tesla, the vortices flowed in straight one-dimensional paths along the steps without snagging on the microscopic defects that normally impede them — an effect the authors describe as pinning-free flow. The team also found that the guiding effect could be dialed up or down by changing the temperature or the field strength, and that at the very lowest temperatures the vortices stopped behaving classically altogether, moving instead by quantum tunneling through energy barriers rather than being thermally jostled over them.

Building on a decade of step-edge physics

The new work extends an older line of research from the same MANA group, which reported in 2014 that single-atom steps in this indium-on-silicon system behave as natural Josephson junctions — the weak links between superconducting regions that allow current to tunnel quantum-mechanically from one side to the other, a phenomenon first described by the Josephson effect in 1962. That earlier discovery established that the steps were electronically special. What the group had not shown until now was that those same steps could be used to herd the vortices themselves — the quantized bundles of magnetic flux first predicted in the 1950s and known today as Abrikosov vortices — into organized, directional traffic.

The paper, "Anisotropic transport of Josephson vortices in atomic-layer superconductors on vicinal surfaces," appeared in Physical Review B on July 30, 2026, with Wenxuan Qian as lead author and Takashi Uchihashi, deputy director of MANA's quantum materials field, as senior author; co-authors included Yash Chauhan, Ryohei Nemoto, Keisuke Sagisaka and Shunsuke Yoshizawa, drawing on affiliations spanning MANA, Hokkaido University, the Institute of Science Tokyo and India's National Institute of Science Education and Research. NIMS posted an institutional research highlight on the work on September 24, and the finding has since moved through specialist outlets including The Quantum Insider's coverage of the MANA release before reaching broader science aggregators this week — a reminder that a summer paper can still generate a fresh news cycle months later as press offices and outlets pick it up in turn.

Why engineers care where a vortex goes

Uncontrolled vortex motion is a central source of dissipation in superconducting devices, converting some of the current's loss-free flow back into ordinary electrical resistance and heat. Engineers building superconducting sensors, quantum circuits or low-power logic have generally fought this problem by trying to pin vortices in place with deliberately introduced defects, which blocks unwanted creep but also blocks any motion that might be useful, such as carrying heat or encoding information through a vortex's position. A surface structure that guides vortices along a chosen path while leaving them otherwise free to move offers a different strategy: control without just clamping down.

Describing the result in the NIMS research highlight, Takashi Uchihashi said the steps' effect on the vortices was unusually clean and strong.

"Our study shows that atomic-scale steps can act as effective rails that guide superconducting vortices," said Takashi Uchihashi, principal investigator at MANA, NIMS.

That framing matters for anyone trying to design superconducting electronics that run colder and cheaper than silicon chips, since real estate at the atomic scale costs nothing to etch — the steps emerge naturally once a crystal is cut at the correct angle. The approach is still a long way from any manufactured device: the measurements were made on a laboratory-grown monolayer at temperatures near absolute zero, conditions far removed from the operating environment of a commercial chip.

What researchers want to test next

The authors frame their result as a demonstration of principle rather than a finished technology, and note in the paper that translating atomic-step guidance into practical superconducting circuitry will require further engineering. Open questions include how the effect scales in other superconducting materials and step geometries, how durable the guiding behavior is away from millikelvin temperatures, and whether the same vicinal-surface approach could be extended to steer heat as well as current, since vortex motion carries both. The quantum-tunneling regime the team observed at the lowest temperatures is also likely to draw separate theoretical interest, since it suggests the steps are shaping not just classical vortex motion but a genuinely quantum transport process — a detail that connects the result to broader efforts to understand two-dimensional quantum phase transitions in ultrathin superconductors.