Probing picosecond depairing currents in type-II superconductors

TL;DR

This study demonstrates that ultrafast picosecond electrical pulses can probe the intrinsic depairing current in type II superconductors, revealing fundamental limits and differences between s-wave and d-wave materials.

Contribution

It introduces a novel ultrafast pulse technique to measure intrinsic depairing currents, surpassing limitations of traditional DC measurements in superconductors.

Findings

Picosecond pulses reach currents up to Jc* >> Jc in NbN.

NbN shows a sharp depairing onset consistent with BCS theory.

YBCO exhibits gradual suppression due to d-wave symmetry.

Abstract

Accessing the intrinsic critical current density (Jc*) in type II superconductors has significant fundamental and technological potential, both as a probe of the microscopic superconducting properties and as a means to increase current limits in high magnetic field devices and in electrical power systems. Yet, the experimental critical current density in type II superconductors (Jc), when measured with DC currents, is generally lower than the intrinsic limit, mostly due to vortex motion and self-heating. Here, we show that ultrafast picosecond electrical pulses, which interact with the material on timescales over which vortices are inertially immobile, carry supercurrents up to the intrinsic depairing limit Jc* >> Jc. We probe picosecond critical currents in NbN and YBa2Cu3O7 (YBCO), as representative s-wave and d-wave superconductors, respectively. In NbN, we find a sharp onset of the picosecond depairing at a current density as large as Jc*=2.2 Jc, a limit that is well described by microscopic dynamics based on BCS theory. In contrast, YBCO exhibits a gradual suppression of superconductivity as a function of the picosecond current, reflecting its d-wave symmetry. These results offer a powerful new probe of superconductors beyond the reach of conventional transport measurements. The ability to reach the depairing current may also lead to robust new platforms for superconducting electronics.