Alternating-current susceptibility, critical-current density, London penetration depth, and edge barrier of type-II superconducting film

From accurate measurements of ac susceptibility, Χ, of a square YBa2Cu3O7-δsuperconducting film of sides 2a = 4 mm and thickness t = 0.25 μm as a function oftemperature T at different values of ac field amplitude Hm and frequency f{hook}, importantsuperconducting properties are extracted and analyzed. The London penetration depthλ(T ) is determined from low-Hm Χ(T) measurements after the Meissner susceptibilityof the square film is calculated numerically by minimizing relevant Gibbs potential.The critical-current density Jc(T ) is extracted from the measured Χ(T,Hm, f) basedon the critical-state and flux-creep models. Having λ(T ) and Jc(T) determined, properlynormalized Χ vs Hm curves are further converted from the measured Χ(T,Hm, f)to be compared directly with the calculated critical-state curve. It is concluded that vortexdynamics is dominated by collective creep, Jc is practically independent of localflux density B, and the contributions from edge barriers to Χ(T,Hm, f) are importantespecially when T approaches Tc. For a more quantitative explanation of the observed Χ(T,Hm, f), type-II superconductivity theory for thin films in a perpendicular magneticfield is developed. Important anomalous phenomena are found and remain openfor further study. © 2012 by Nova Science Publishers, Inc. All rights reserved.