Deep inside a superconductor, where electricity flows without loss, tiny magnetic whirlpools called vortices form when strong fields press against the material, and they quietly drain energy whenever they move. In a laboratory in Tallinn, researchers working with colleagues at Rutgers used invisible terahertz light to look into these hidden cores and learned that the particles trapped within them are not all alike. It is a small discovery with large consequences, because the machines that depend on superconductors, from hospital scanners to particle accelerators, are limited by exactly this ki
Terahertz Light Maps the Hidden Particles Inside Superconductor Vortices
Two materials that look alike on paper can differ deep inside their vortices
Mark
So what did they actually manage to see that nobody had before?
Mimi
Two groups of particles trapped inside the vortices, told apart. Earlier experiments had found the energy levels, but couldn't separate who was contributing what.
Mark
How does light do the separating?
Mimi
Through handedness. One group responds to left-handed polarized terahertz light, the other to right-handed. Same film, two distinct signals.
Luke
Worth noting the particle ratios, nearly four to one in one sample and about equal in the other, come from calculations built on those measurements, not from counting particles directly.
Mark
Why does the selenium comparison matter?
Mimi
Both films became superconducting at almost the same temperature. A standard test would call them similar, yet their insides differ.
Luke
Fair, but the source doesn't say which composition performs better in a magnetic field. That link isn't established here.
Mark
And the bigger payoff?
Mimi
Vortex motion wastes energy, so knowing what's inside could help design materials that hold up in strong fields, like MRI magnets.
Luke
That's the stated motivation. No new material has been built from this yet, and it only works for superconductors with narrow vortex cores.
Der Puls
- Magnetic whirlpools inside superconductors are bleeding energy every time they shift, and that loss caps how well these materials can perform in strong fields.
- Researchers cooled ultrathin iron-based films to extreme cold and bombarded them with invisible terahertz light to peer into vortex cores.
- The light's twist, clockwise or counterclockwise, revealed two distinct particle groups that had previously blurred together in measurements.
- Changing only the selenium content in the film produced different particle mixes and energy gaps despite nearly identical superconducting temperatures, showing materials can differ hidden within.
- The method now offers a path to screening other superconductors with narrow vortex cores, aiming toward more dependable electrical materials.
Deep inside a superconductor, where electricity flows without loss, tiny magnetic whirlpools called vortices form when strong fields press against the material, and they quietly drain energy whenever they move. In a laboratory in Tallinn, researchers working with colleagues at Rutgers used invisible terahertz light to look into these hidden cores and learned that the particles trapped within them are not all alike. It is a small discovery with large consequences, because the machines that depend on superconductors, from hospital scanners to particle accelerators, are limited by exactly this kind of unseen motion. Understanding what the vortices hold is a step toward materials that can carry greater power with greater reliability.
In a laboratory at the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia, researchers cooled very thin films to about minus 438 degrees Fahrenheit, placed them in powerful magnetic fields, and sent terahertz radiation through them. Their target was the interior of vortices, small magnetic whirlpools that form inside superconductors. The work, a collaboration with scientists at Rutgers, appears in Physical Review Letters.
Superconductors carry electricity without losing energy as heat, which is why they power MRI scanners and particle accelerators. Yet when magnetic fields create vortices within them, and those vortices move, energy escapes. Girsh Blumberg of Rutgers explained that understanding what vortices contain is essential to improving these materials. He likened the material to Swiss cheese, with the vortices as the holes.
Particles trapped in those holes follow quantum rules, occupying separate energy levels like rungs of a ladder. The team chose an iron-based superconductor because its narrow vortex cores keep those levels distinct enough to measure. The films, built atom by atom from iron, tellurium and selenium, were only 40 nanometers thick and had to be extremely clean, since any imperfection could hide the signals.
As the terahertz light passed through, its polarization shifted. One group of particles responded to left-handed twisting, the other to right-handed, allowing each group to be studied separately. Comparing two films with different selenium amounts revealed that identical superconducting temperatures can conceal very different particle mixes inside. The researchers hope the approach can be extended to other superconductors, helping engineers design more reliable electrical materials.
In a laboratory at the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia, researchers cooled thin films to about minus 438 degrees Fahrenheit, placed them in powerful magnetic fields, and sent terahertz radiation, a form of invisible light, through them. What they were measuring was the contents of vortices, tiny magnetic whirlpools that form inside a superconductor. The work, by scientists at Rutgers and in Estonia, appears in Physical Review Letters.
A vortex is circulating electrical current around a narrow core where superconductivity is weakened, while the material around it stays superconducting. Superconductors carry electricity without losing energy as heat, which is why they are used to make powerful magnets in MRI scanners and particle accelerators. But magnetic fields can create vortices inside many of them, and when vortices move, energy is lost. Girsh Blumberg, a Distinguished Professor in the Department of Physics and Astronomy at Rutgers and a co-author, said researchers need to understand what vortices contain and how they behave in order to improve these materials. He compared the material to Swiss cheese, with the vortices as the holes.
Particles confined in those holes obey quantum physics. In 1964, physicists predicted they would occupy separate energy levels, something like the rungs of a ladder, and that a particle could climb from one rung to another by absorbing the right amount of energy. Earlier experiments had detected these states. Blumberg and his colleagues wanted to study the transitions between them and separate the contributions of different groups of particles.
The choice of material mattered. In many conventional superconductors the energy levels sit so close together that their signals blur. The team chose an iron-based superconductor whose vortex cores are narrow, which keeps the levels far enough apart to tell apart.
The films were prepared by the Rutgers team, including Seongshik Oh, a professor of physics and astronomy, and postdoctoral research associate Hee Taek Yi. They built each film by controlled, atom-by-atom layering of iron, tellurium and selenium, to a thickness of 40 nanometers, roughly a thousandth of the width of a human hair. Blumberg said the experiment demanded extremely clean, thin films, because imperfections can disturb the particles' behavior and hide their signals. The films also had to be thin enough for light to pass through them.
The researchers then tracked how the terahertz light's polarization, the orientation of its electric field, changed on passage. Light can twist in a clockwise or counterclockwise pattern. One group of trapped particles responded to the left-handed pattern and the other to the right-handed one, which let the team distinguish and study each group on its own. Blumberg said that looking for the transitions with light of different handedness is what separates them.
From the measurements and mathematical calculations, the team 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 destroy superconductivity for each group.
They compared two versions of the film with different amounts of selenium. Both became superconducting at nearly the same temperature, yet the recipe change altered the mix of particles in the vortices. In one sample, the calculations suggested nearly four particles of one group for every one of the other; in the second, the groups were about equal. The recipe also changed how much energy the particles needed to jump between levels and how quickly their light responses faded. Materials with similar superconducting temperatures, in other words, can differ substantially inside.
The authors say the approach could be applied to other superconductors with sufficiently narrow vortex cores. Blumberg noted that earlier methods could detect the trapped states but could not reveal the difference between the two groups as directly. The collaboration was supported by the National Science Foundation and the European Research Council.
Bemerkenswerte Zitate
To improve superconductors, scientists need to understand what vortices contain and how they behave.— Girsh Blumberg, Rutgers Distinguished Professor of Physics and Astronomy
By looking for these transitions with light of different handedness, you can separate them.— Girsh Blumberg
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