Max Planck Institute reveals fundamental current limits in superconductors

Researchers observed distinct current thresholds in two superconductors using ultrashort pulses, revealing how Cooper pairs break apart.

On October 2, 2026, scientists at the Max Planck Institute for the Structure and Dynamics of Matter applied ultrashort electrical pulses—generated by photoconductive switches triggered by 300-femtosecond green laser pulses at 515 nanometers—to test superconductors. The method enabled them to probe microscopic properties hidden from conventional measurements. They observed that niobium nitride (NbN), an s-wave superconductor, remained superconducting beyond its conventional critical current limit until a distinct threshold where Cooper pairs began breaking apart. Yttrium barium copper oxide (YBCO), a d-wave superconductor, exhibited progressive weakening of superconductivity as current increased, with its state gradually degrading due to directional energy gap variations. The study identified the depairing current as the fundamental limit where Cooper pairs separate—a threshold that conventional DC transport measurements cannot access because vortices typically cause failure before reaching this intrinsic limit.

This technique provides the first direct observation of how different superconductors respond to extreme current levels. By revealing NbN’s abrupt depairing and YBCO’s gradual degradation, the research clarifies the quantum mechanisms that govern superconductivity under conditions previously unmeasurable.

For energy access, this work advances understanding of superconductors’ intrinsic limits. Future materials designed to avoid vortex-induced failure could achieve higher current stability, potentially reducing energy loss in power transmission. However, the findings apply only to NbN and YBCO, and broader applicability requires testing additional materials.

What to watch: Wider validation of depairing thresholds across superconducting materials. The study notes results require further testing to determine broader relevance—only two materials were examined, and the technique’s scalability for real-world applications remains unproven.

Source: ScienceDaily