Depinning of caged interstitial vortices in superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>a</mml:mi></mml:math>- WGe films with an antidot lattice

Abstract

The magnetoresistance, critical currents, and voltage-current ($V\ensuremath{-}I$) characteristics have been studied in superconducting $a$-WGe films with a square lattice of cylindrical microholes (antidots). Besides a strong enhancement of the critical current caused by matching of the flux lines with the antidot lattice having a period $d$, two different dissipative regimes have been observed giving rise to a crossover in the [$log(V)\ensuremath{-}log(I)$] characteristics for magnetic fields above the first matching field ${B}_{1}={B}_{\ensuremath{\varphi}}\ensuremath{\equiv}{\ensuremath{\Phi}}_{0}{d}^{\ensuremath{-}2}$. This $V\ensuremath{-}I$ behavior is caused by the coexistence of a weakly pinned interstitial vortex fluid and a strongly pinned vortex lattice at the antidots.