We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edgepinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK (B) = JpK (0)/(1 + |B|/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK (B). We find that Jc(Ba) is very nearly equal to JpK (Ba) when Ba ≥ B * a , where B * a is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK (Ba) at low fields when Ba < B * a , with the largest suppression occurring when B * a /B0 is of order unity or larger.

We present general solutions for the Meissner-state magnetic-field and current-density distributions for a pair of parallel, coplanar superconducting strips carrying arbitrary but subcritical currents in a perpendicular magnetic field. From these solutions we calculate (a) the inductance per unit length when the strips carry equal and opposite currents, (b) flux focusing in an applied field—how much flux per unit length is focused into the slot between the two strips when each strip carries no net current, (c) the current distribution for the zero-flux quantum state when the strips are connected with superconducting links at the ends and (d) the current and field distributions around both strips when only one of the strips carries a net current. The solutions are closely related to those found recently for the magnetic-field and current-density distributions in a thin, bulk-pinning-free, type-II superconducting strip with a geometrical barrier when the strip carries a current in a perpendicular applied field.

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Abstract. We calculate the magnetic-field dependence of the critical current due to both geometrical edge barriers and bulk pinning in a periodic coplanar array of narrow superconducting strips. We find that in zero or low applied magnetic fields the critical current can be considerably enhanced by the edge barriers, but in modest applied magnetic fields the critical current reduces to that due to bulk pinning alone.

We present analytic solutions for the Meissner-state magnetic-field and current-density distributions for four long parallel coplanar superconducting strips carrying subcritical currents in a perpendicular magnetic field when there is no net magnetic flux through the two slots between the outermost strips. We make use of these solutions to investigate the flux-focusing effect; i.e., we calculate how much magnetic flux per unit length is focused into the central slot when the strips are in a perpendicular magnetic field Ha = Ba/μ0 and the outermost pairs of strips carry no net current. We also calculate the inductance per unit length of the system when the net current flowing in the two right strips is equal in magnitude and but opposite in direction to the net current flowing in the two left strips. We show that for narrow superconducting strips mutual-inductance calculations based on exact results for two strips provide good approximations to our exact results for four strips.

The surface barrier effects in type H superconductors with high GinzburgLandau parameter are studied and the associated barrier field effects are considered as being due to the interactions between the vortex line and the associated screening currents with the external magnetic field and the surface of the specimen. Moreover, it is demonstrated that the penetration depth depends on the external field and the thickness of material and also that the order parameter is completely quenched at the sample surfaces for the applied field equal to the barrier field.