Direct evidence for filamentary and channel vortex flow in Pb/In superconducting films

Filamentary vortex flow in thin Pb/(14 at. %)In films is revealed by multiple voltage jumps in current-voltage (IV) characteristics below a critical magnetic field much lower than the upper critical field B-c2. The voltage jumps exhibit large counterclockwise hysteresis which diminishes with increasing field leading to bistable behavior close to the onset of free-flux flow. From the magnetic field and temperature dependence of the jump heights and currents at which jumps occur we infer that the number of flux lines in each channel or filament remains constant. In this regime, where the shear modulus of the vortex lattice is negligible, we find a nearly parabolic dependence of the depinning force on magnetic field, which is a signature of channel vortex motion. [S0163-1829(99)50710-8].