Vortex dynamics at high velocities and proximity effect in superconducting thin films

The vortex dynamics at high velocities in niobium and niobium/gold thin films is studied by taking notice of the role of the metallic layer. The proximity effect and its influence on superconducting properties is first identified. We report then in a flux flow regime an abrupt transition to the normal state which has been predicted theoretically by Larkin and Ovchinnikov. The influence of the metallic layer on the parameters of this instability is studied. It demonstrates that the gold film decreases the critical force and the vortex velocity driving the transition. [Copyright &y& Elsevier]