Novel pinning phenomena in a superconducting film with a square lattice of artificial pinning centers

TL;DR

This study reveals a novel current-dependent pinning phenomenon in a superconducting Nb film with artificial pinning centers, where the differential resistance behavior at matching fields reverses as the dc current increases.

Contribution

It uncovers a new pinning behavior in superconducting films with artificial pinning centers, showing a current-induced reversal of resistance anomalies near the transition temperature.

Findings

Differential resistance shows a minimum at matching fields at low currents.

At higher currents, the differential resistance exhibits a maximum at matching fields.

The flux flow mode likely changes with increasing dc current.

Abstract

We study the transport properties of a superconducting Nb film with a square lattice of artificial pinning centers (APCs) as a function of dc current, at a temperature close to the superconducting transition temperature of the film. We find that, at low dc currents, the differential resistance of the film shows the standard matching field anomaly, that is, the differential resistance has a local minimum at magnetic fields corresponding to an integer number of flux lines per APC. However, at higher dc currents, the differential resistance at each matching field turns to a local maximum, which is exactly opposite to the low current behavior. This novel effect might indicate that the flux lines in the APC system change their flow mode as the dc current is increased.