Physics – Condensed Matter – Superconductivity
Scientific paper
2010-06-11
Phys. Rev. B 82, 024512 (2010)
Physics
Condensed Matter
Superconductivity
Scientific paper
10.1103/PhysRevB.82.024512
We measure current-voltage characteristics as function of magnetic field and temperature in Nb strips of different thickness and width. The instability voltage of the flux flow state related to the vortex critical velocity v* is studied and compared with the Larkin-Ovchinnikov theory. Beside the usual power-law dependence v* ~ B^-1/2, in the low field range a new cross-over field, Bcr1, is observed below which v* decreases by further lowering the external magnetic field B. We ascribe this unexpected cross-over to vortex channeling due to a fan-like penetration of the applied magnetic field as confirmed by magneto-optic imaging. The observation of Bcr1 becomes a direct evidence of a general feature in type-II superconducting films at low fields, that is a channel-like vortex motion induced by the inhomogeneous magnetic state caused by the relatively strong pinning.
Grimaldi G.
Laviano Francesco
Leo A.
Mezzetti Emilia
Nigro Alessandro
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