MAGNETIC SELF-FIELD ENTRY INTO A CURRENT-CARRYING TYPE-II SUPERCONDUCTOR

A problem of the irreversible entry of the Abrikosov vortex ring, indu ced by the self-field of a transport current, into a long type-II supe rconductor cylinder of arbitrary radius R is solved exactly in the Lon don approximation. The magnetic field and current distribution for the toroidal vortex inside the cylinder are evaluated. The Gibbs free ene rgy of the system is calculated when the transport current is applied. The critical current j(c) of a spontaneous vortex penetration into th e superconductor through a surface Bean-Livingston barrier is found to be independent of the radius of the cylinder and close to the depairi ng current. However, the dependence of the width of edge barrier on th e transport current in a thin cylinder is found to differ qualitativel y from that in a thick cylinder. As a result of this, in the first cas e there is no characteristic current but j(c), while in the second cas e a characteristic current j(c1) congruent-to j(c)/K arises (kappa the Ginzburg-Landau parameter) at which the barrier width drops down to v alues of the order of the magnetic-field-penetration depth lambda, whi ch allows for vortex entry on the surface defects of the size of lambd a. The latter result is discussed in reference to the high-critical-cu rrent observations on the microbridges of high-temperature superconduc tors.