Picosecond Current Pulses Expose the Hidden Depairing Limit in Superconductors
Probing picosecond depairing currents in type-II superconductors
Physicists have long sought to measure the depairing current density Jc*, the fundamental limit where Cooper pairs break, but vortex motion and heating obscure it. Using picosecond electrical pulses, researchers froze vortices and directly observed depairing in both s-wave NbN and d-wave YBCO. At 6.5 times the conventional critical current, the superconducting response vanished, revealing an intrinsic material limit that could guide faster superconducting electronics.
The core idea is that, within picosecond timescales, the penetration of vortices is inertially frozen near the edges, as their speed is intrinsically limited to tens of nanometres per picosecond.