Theory of the longitudinal vortex-shaking effect in superconducting strips

We show that for a thin superconducting strip placed in a perpendicular dc magnetic field—the typical geometry of experiments with high-$T_c$ superconductors—the application of a weak ac magnetic field along the strip (i.e., perpendicular to the dc field and parallel to the circulating critical currents) generates a dc voltage in the strip, which causes the critical currents and irreversible magnetic moment to relax completely. This relaxation process is not due to thermally activated flux creep but to the drift of vortices towards the center of the strip under the influence of the ac field. This longitudinal vortex-shaking theory supplements our previous theory of transverse vortex shaking where the ac field was perpendicular to the irreversible currents. Together, both theories clarify the nature of the vortex-shaking effect in real superconducting samples of finite length.