Ultrafast current pulses let scientists push superconductors beyond their usual experimental limits before vortices and heat could interfere.
The method revealed striking differences in how two superconducting materials break down and could expose quantum behavior that conventional measurements miss.
Superconductivity is one of the most remarkable behaviors found in quantum materials. When some materials are cooled below a specific transition temperature, their electrical resistance disappears, allowing current to move through them without losing energy as heat.
This happens because electrons pair up to form what are known as Cooper pairs. These paired electrons move together through the material as part of a coordinated quantum state. That ability makes superconductors valuable for technologies including powerful magnets, highly sensitive detectors, and quantum circuits.
But superconductivity cannot survive unlimited electrical current. If the current becomes too strong, resistance eventually appears, and the superconducting state breaks down. The current level at which this begins is known as the critical current.
Why Superconductors Usually Fail Early
In type II superconductors, the experimentally measured critical current often does not reflect the true microscopic limit of superconductivity itself.
Instead, the limit is usually set by vortices, tiny regions where magnetic flux penetrates the material. As the electrical current rises, these vortices can begin to move. Their motion creates resistance and heat, which can destroy the superconducting state before the material reaches its deeper intrinsic limit.
That higher limit is known as the depairing current.
“One way to picture it is that the current “twists” the phase of the coherent quantum state of the superconductor, rather like winding a spring,” explains Eryin Wang, lead author of the study.
If that quantum state is twisted too strongly, it becomes unstable. At the depairing threshold, the Cooper pairs responsible for superconductivity begin to separate.
Conventional direct-current (DC) transport measurements have difficulty reaching this point because vortex motion and heating usually interfere first.
Outrunning the Vortices
The researchers tackled the problem by making the electrical current extremely brief.
“Our strategy was to outrun the vortex dynamics,” says Eryin Wang.
Vortices typically travel at speeds of tens of kilometers per second. That sounds fast, but during a single picosecond they move only tens of nanometers. By delivering current over an extremely short interval, the researchers could reach very high current densities before the vortices had enough time to move significantly or heat the sample.
This approach sharply reduces energy loss caused by vortex motion and makes it possible to drive the superconducting state much closer to its intrinsic current limit.
Electrical Pulses Lasting Just Picoseconds
To create these ultrashort bursts of current, the team used an ultrafast electrical transport platform developed at MPSD.
“To apply current to superconductors for only a few picoseconds, we used the ultrafast electrical-transport platform that we have been developing at our institute,” says Guido Meier, co-author of the study.
The system uses photoconductive switches triggered by 300-femtosecond green laser pulses with a wavelength of 515 nanometers. Once activated, the switches produce electrical pulses lasting only a few picoseconds.
Those pulses travel through a coplanar waveguide and then pass through superconducting samples only micrometers in size.
Two Superconductors Behave Very Differently
The researchers tested two materials, NbN and YBCO, because their superconducting states have fundamentally different structures.
NbN has a relatively uniform superconducting energy gap (s-wave), while YBCO has a gap that depends strongly on direction (d-wave). Comparing the two allowed the scientists to investigate how these microscopic differences affect what happens when superconductors are driven with extremely strong, ultrafast currents.
NbN remained superconducting until the current reached a clear threshold that was far above its conventional DC critical current. Once that point was crossed, the material’s response changed sharply, providing evidence that the Cooper pairs were beginning to break apart.
YBCO behaved differently. Rather than remaining stable and then suddenly collapsing, its superconducting state weakened progressively as the current increased.
The researchers attribute this difference to the materials’ underlying superconducting structures. In NbN, the energy gap is almost uniform in every direction. In YBCO, the gap varies strongly with direction and falls to zero along particular directions.
Because of that structure, superconductivity in YBCO can gradually weaken instead of failing at one sharply defined threshold.
A New Window Into Superconductivity
“Our results suggest that picosecond transport can provide access to microscopic properties of superconductors, including their gap symmetry, that are not directly available from conventional DC transport,” says Andrea Cavalleri, who leads the research group.
The researchers caution that more superconducting materials will need to be tested before they can determine how broadly the connection applies.
Still, the findings show that ultrashort electrical pulses can reveal forms of superconducting behavior that conventional experiments usually cannot reach. By acting faster than vortex motion and heating, the technique gives scientists a way to study superconductors closer to their natural microscopic timescales.
That could provide new tools for investigating and controlling superconducting states while opening access to a regime of ultra-high current superconductivity. In the future, such capabilities could also have implications for optoelectronics and potentially magnetic devices.
Reference: “Probing picosecond depairing currents in type-II superconductors” by E. Wang, M. Chavez-Cervantes, J. Satapathy, T. Matsuyama, G. Meier, X. Zhang, L. You, F. Marijanovic, J. B. Curtis, E. Demler and A. Cavalleri, 24 September 2026, Nature Physics.
DOI: 10.1038/s41567-026-03469-z
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