Depinning of caged interstitial vortices in superconductinga- WGe films with an antidot lattice

The magnetoresistance, critical currents, and voltage-current ($V-I$) 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 [$log\mathrm{}\left(V\right)-log\mathrm{}\left(I\right)\mathrm{}$] characteristics for magnetic fields above the first matching field $B_1=B_{\phi }\equiv {\Phi }_0{d}^{-2\mathrm{}}$. This $V-I$ behavior is caused by the coexistence of a weakly pinned interstitial vortex fluid and a strongly pinned vortex lattice at the antidots.