Accessing the intrinsic depairing current density in type-II superconductors is prevented in d.c. transport by vortex motion and self-heating. Picosecond electrical pulses, whose ~2 ps full-width-at-half-maximum duration is too short for vortices (which move only tens of nm per ps) to penetrate and dissipate energy, drive supercurrents up to the thermodynamic depairing limit. Experiments used coplanar-waveguide devices with photoconductive switches to launch and sample pulses through thin-film samples: a ~20 nm NbN s-wave film (conventional Jc ≈ 100 GA m−2 at 7 K) and YBa2Cu3O7 (YBCO) d-wave film (conventional Jc ≲ 50 GA m−2 at 50 K). The depairing condition corresponds microscopically to a quasiparticle energy shift ħkF·vs reaching the superconducting gap Δ.
Measurements reveal qualitatively different dynamics tied to pairing symmetry. NbN shows a sharp onset of picosecond depairing at a current density ≈2.2× the conventional critical current, consistent with Bardeen-Cooper-Schrieffer predictions for s-wave depairing. YBCO exhibits a gradual suppression of superconductivity as current increases, reflecting nodal d-wave gap structure. The technique therefore provides a direct transport probe of intrinsic depairing beyond conventional limits and suggests a route to operate superconducting electronics closer to fundamental current-density limits.
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