Experimental determination of the number of flux lines trapped by micro-holes in superconducting samples

TL;DR

This study uses ac-susceptibility measurements to determine how many flux quanta are trapped by micro-holes in superconducting Pb films, revealing dynamic regimes and pinning effects.

Contribution

It provides a novel experimental method to accurately determine the maximum number of flux quanta trapped by micro-holes in superconductors.

Findings

Identification of different vortex dynamic regimes via ac-susceptibility

Observation of characteristic features indicating flux quanta trapping

Clear determination of maximum flux quanta per hole

Abstract

The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac-susceptibility measurements. For different amplitudes h of the ac-drive, the ac-susceptibility x=x'+ix'' exhibits a complex field dependence associated with different dynamic regimes. At very low ac-drives where both, multiquanta vortices trapped by the antidots and interstitial vortices oscillate inside the pinning potential (intra-valley motion), a small kink in x'(H) together with a very low dissipation is observed. At intermediate ac-excitations such that vortices in the antidots remain pinned whereas interstices are driven out of the pinning well, a more pronounced kink in the screening coinciding with the onset of dissipation (x''(H) ~ 0) indicates the entrance of interstitial vortices. Eventually, at high enough amplitudes all vortices are set in motion and the penetration of interstitial vortices appears as a sudden reduction of the shielding power. We show that these distinctive features allow us to clearly identify the maximum number of flux quanta per hole regardless the vortex dynamic regime.