Fluctuation Effects on a Strongly Pinned Vortex Lattice in a Thin Type-II Superconducting Wire

We report on transport properties of the vortex lattice in fine, round NbTi wires fabricated by a novel wire-drawing process. The voltage onset in the isothermal $I-V$ characteristic is sharp for thick wires ($d\ge 1$ μm) at 4.2 K and 6 T, but is rounded for thinner wires. The thinnest wires also display an Ohmic resistivity at low current densities. This linear resistivity decreases exponentially with temperature near $T_c\mathrm{}\left(H\right)\mathrm{}$ and approaches a constant value at low temperatures. We explain our results as finite size effects of the thermal and quantum collective creep of vortex lines.