Electron Drag and Flow Stress in Niobium and Lead at 4.2°K

It has been found that the flow stresses of superconducting niobium and lead at 4.2^∘{}K increase in the transition between superconducting and normal states produced by an external magnetic field. The ratio of the increment to the flow stress in the superconducting state is 2.9% in lead and 0.6% in niobium. It is concluded that the conduction electrons in the normal metals are impeditive for the motion of dislocations.