Abstract
Nondestructive, AC inductive methods detecting third-harmonic voltages are widely used to measure the distribution
of local critical current densities Jc of superconducting films deposited on large-area single-crystal substrates. We have extended
this method to determine the electric field E versus current density J relation and the n-value (index of the power-law E-J
characteristics) by evaluating the dependence of Jc on measurement frequency. The method to determine Jc with an electric-field
criterion has been established as an international standard. This convenient method can also be applied to coated conductors with
metallic substrates. Magnetic-field angular dependent Jc measurements are possible, and such measurements are of practical importance in applying coated conductors to superconducting coils. They are also useful in investigating the flux pinning mechanism. In this focused review, we briefly introduce the measuring method that has been based on our long years of research, and describe the precautionary points when recent coated conductors with high critical currents per unit width are measured.
