Theory of Pinning Effect on the Nonlinear Resistance in the Mixed State of Type II Superconductors

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Abstract
A mechanism is proposed for the nonlinear flux flow resistance in the mixed state of type II superconductors. Beside of the frictional drag which is responsible to the linear resistance, the flux line motion is subjected to the pinning effects, which are appreciable especially when the Lorentz-like driving force is small, that is to say, in the small current region. The flux line is pinned down for a time τ r , which decreases with the increase of the Lorentz-like force, at each pinning center and for the rest time τ r , no voltage appears while the currents flow. The dislocation-immigration analogue in the imperfect lattice is used for the line motion to calculate τ r and the result shows the nonlinear resistance in good agreement with the experimental results.