Self field of ac current reveals voltage-current law in type-II superconductors

The distribution of ac magnetic fields in a thin superconducting strip is calculated when an ac current is applied to the sample. The edge barrier of the strip to flux penetration and exit is taken into account. The obtained formulas provide a basis to extract voltage-current characteristics in the bulk and at the edges of superconductors from the measured ac magnetic fields. Based on these results, we explain the spatial and temperature dependences of the profiles of the ac magnetic field measured in a ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8}$ strip [D.T. Fuchs et al., Nature (London) 391, 373 (1998)].