Non-reciprocity of Vortex-limited Critical Current in Conventional Superconducting Micro-bridges

TL;DR

This study demonstrates a superconducting diode effect in NbN micro-bridges caused by vortex surface barriers, with significant diode efficiency and potential for practical applications over a broad temperature range.

Contribution

It reveals that vortex surface barriers cause non-reciprocal critical currents in NbN micro-bridges, advancing understanding of superconducting diode effects.

Findings

Diode efficiency of approximately 30% under small out-of-plane magnetic fields.

The diode effect vanishes when magnetic field is parallel to the sample plane.

Rectification persists up to about 10 K, indicating potential for practical devices.

Abstract

Non-reciprocity in the critical current has been observed in a variety of superconducting systems and has been called the superconducting diode effect. The origin underlying the effect depends on the symmetry breaking mechanisms at play. We investigate superconducting micro bridges of NbN and also NbN/magnetic insulator (MI) hybrids. We observe a large diode efficiency of $\approx$~30\% when an out-of-plane magnetic field as small as 25~mT is applied. In both NbN and NbN/MI hybrid, we find that the diode effect vanishes when the magnetic field is parallel to the sample plane. Our observations are consistent with the critical current being determined by the vortex surface barrier. Unequal barriers on the two edges of the superconductor strip result in the diode effect. Furthermore, the rectification is observed up to a temperature $\sim$10~K, which makes the device potential for diode based applications over larger temperature range than before.