Ac susceptibility of a melt-textured YBa_2Cu_3O_x ring closed by a strong-coupling contact

摘要

The complex ac susceptibility χ=χ′-jχ″ of a melt-textured YBa_2Cu_3O_x ring closed by a strong-coupling contact is measured after zero-field cooling to 77 K as a function ,of the ac field amplitude H_m and frequency f. The resulting χ(H_m,f) is similar to that derived from a power-law relation between the local current density and electric field but with maximum χ″(H_m) increasing steadily with increasing f, which is explained by the creep of Abrikosov-Josephson vortices along the contact driven by the London force of supercurrents and the Lorentz force of the induced normal currents.