Study of the relationship between theV-I curve and the flux dynamics in superconductors

Abstract

The equivalence of the experimental V-I characteristic(V∝Im) and the material E-j curve (E∝jn)was studied. We show numerically that only when the current I islarger than Ihom, the fully penetrating current, can theV-I curve be equivalent to the E-j one and thus be used todetermine the material parameter n, whereas if I<Ihom, jis inhomogeneous and the V-I curve is not appropriate for usein probing the properties of the sample. The inhomogeneity of jcan be checked by simply measuring the voltage relaxation curve at agiven I. Furthermore, it is shown that Ihom varies withdI/dt and n. The dependence of Ihom on dI/dt indicates that current cannot go directly into ahomogeneous region in practical transport measurements. Moreover,we argue that all of the V-I curves with different values ofthe flux-creep barrier exponent µ merge at large current.Since current is probably inhomogeneous in the small-current region,the V-I curve might not be appropriate for use in studying theproperties of the sample in this region. Therefore, the V-Icurve may not be appropriate for determining µ in theU-j relation at all sensitively.