Invisible Light Reveals Hidden Particle States Inside Superconductor Vortices

Scientists at Rutgers University and in Estonia have used invisible light to peer inside tiny magnetic whirlpools, called vortices, within a superconductor, revealing details that conventional techniques could not readily separate. Their study, published in Physical Review Letters, distinguishes two groups of particles trapped within those vortices and measures properties that earlier methods could only detect in a blurred, combined form. The work offers a new way to understand the materials used in powerful magnets, from MRI scanners to particle accelerators.

Superconductors can carry electricity without losing energy as heat, which makes them essential for creating the powerful magnets used in medical imaging and particle physics. But magnetic fields can produce tiny vortices inside many superconductors. When these vortices move, they cause energy losses. Understanding what the vortices contain and how they behave could help scientists develop materials that perform more reliably in strong magnetic fields. “To improve superconductors, scientists need to understand what vortices contain and how they behave,” said Girsh Blumberg, a Distinguished Professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences and a co-author of the study. “This study provides a new way to look inside them.”

Each vortex consists of circulating electrical current around a narrow core where superconductivity is weakened, while the surrounding material remains superconducting. Blumberg compared the structure to Swiss cheese, with many holes, where the holes are the vortices. Particles confined within them follow the rules of quantum physics, which govern matter at extremely small scales. In 1964, physicists predicted that these trapped particles would occupy separate energy levels, resembling the rungs of a ladder. A particle can move from one allowed level to another by absorbing the right amount of energy. Earlier experiments had detected these states, but Blumberg and his colleagues wanted to learn more about the transitions between them and to distinguish the contributions of different groups of particles.

Finding a suitable material was essential. In many conventional superconductors, the energy levels are packed so closely together that their signals blur. The iron-based superconductors the team chose have narrow vortex cores, which help keep the levels far enough apart to distinguish. The experiment depended on thin superconducting films prepared by the Rutgers team, which included Seongshik Oh, a professor in the Department of Physics and Astronomy, and Hee Taek Yi, a postdoctoral research associate. The films were made by controlled atomic layer-by-layer deposition of iron, tellurium and selenium, and each was 40 nanometers thick, roughly a thousand times thinner than a human hair. A nanometer is one-billionth of a meter.

“We need extremely clean films, thin and clean films, to do that experiment,” Blumberg said. Imperfections can interfere with the particles’ behavior and obscure their signals. The films also had to be thin enough for the researchers to measure light passing through them. These demanding requirements shaped the entire experiment, because any structural flaw in the material would have scrambled the delicate quantum signatures the team was trying to observe within the vortex cores.

The light measurements took place at the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia. Researchers cooled the samples and exposed them to powerful magnetic fields, and both samples became superconducting at about minus 438 degrees Fahrenheit. The team then passed terahertz radiation, a form of invisible light, through the films and measured changes in the light’s polarization, the orientation of its electric field. Light waves can vibrate in a pattern that turns clockwise or counterclockwise. One group of particles responded to the left-handed light pattern, while the other group responded to the opposite, right-handed, pattern. That difference allowed the researchers to tell the two groups apart and study each one separately.

“By looking for these transitions with light of different handedness, you can separate them,” Blumberg said. Using their light measurements together with mathematical calculations, the researchers estimated the size of the vortices and how long the particles’ responses to light lasted. They also estimated how strongly the vortices resist changes in speed or direction, and how strong a magnetic field would be needed to disrupt superconductivity for each group of particles. These quantities, which had previously been entangled in conventional measurements, could now be assigned to each particle group individually.

Members of the team compared two versions of the material containing different amounts of selenium. Both began carrying electricity without resistance at almost the same temperature. But changing the recipe changed the mix of particles trapped inside the vortices. In one sample, the calculations suggested there were nearly four particles of one group for every particle of the other. In the second sample, the two groups were about equal in number. Changing the composition also changed how much energy the particles needed to jump between levels and how quickly their responses to the light faded.

The comparison shows how materials with similar superconducting temperatures can have substantially different internal properties. The technique gives scientists a way to examine those differences as they change a material’s composition, providing a sensitive probe of the microscopic physics that bulk measurements alone cannot resolve. The authors said the approach could be used to investigate other superconductors with sufficiently narrow vortex cores, expanding the tools available to researchers developing new materials for demanding magnetic applications.

“The technique is especially useful because it can separate the contributions of two different groups of particles,” Blumberg said. “Earlier methods could detect the trapped states but could not reveal this difference as directly.” The international research collaboration was supported by the National Science Foundation and by the European Research Council. The study, an observational study published in Physical Review Letters on 23 October 2026 under the title “Chirality-Resolved Spectroscopy of Caroli–de Gennes–Matricon States in Multiband FeTe1−xSex Superconductors,” demonstrates how a carefully engineered thin film, cooled to near absolute zero and probed with handed terahertz light, can turn the hidden interiors of magnetic vortices into measurable, distinguishable quantum systems.

Subject of Research: Chirality-resolved terahertz spectroscopy of quantum particles trapped in magnetic vortices of iron-based superconductors

Article Title: Scientists use light to reveal the hidden workings of superconductors

Article References: Scientists use light to reveal the hidden workings of superconductors. Original publication (Bibliographic details unavailable.)

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Keywords: superconductors, magnetic vortices, terahertz spectroscopy, quantum physics, iron-based superconductors, Physical Review Letters, Rutgers University, thin films, energy levels, polarization, quantized vortex states, materials science