Mixed superconducting state without applied magnetic field

A superconducting (SC) mixed state occurs in type-II superconductors where the upper critical field ${H}_{c2}$ is higher than thermodynamic ${H}_{c}$. When an applied between these fields, free energy depends weakly on order parameter which therefore can be small (SC state) or zero (normal at different parts of sample. In this paper we demonstrate how a normal along line traversing superconductor turned and off externally field. The concept based long, current-carrying excitation coil, piercing ring-shaped superconductor. ring experiences field, but vector potential produced by coil generates circular current that destroys superconductivity radial starting preexisting nucleation points Unlike destruction with magnetic method reversible reproducible; full recovered upon removing from cooldowns yield same lines. We suggest applications magnetic-field-free state.