Predicted field-dependent increase of critical currents in asymmetric superconducting nanocircuits

Abstract

The critical current of a thin superconducting strip of width $W$ much larger than the Ginzburg-Landau coherence length $\ensuremath{\xi}$ but much smaller than the Pearl length $\ensuremath{\Lambda}=2{\ensuremath{\lambda}}^{2}/d$ is maximized when the strip is straight with defect-free edges. When a perpendicular magnetic field is applied to a long straight strip, the critical current initially decreases linearly with $H$ but then decreases more slowly with $H$ when vortices or antivortices are forced into the strip. However, in a superconducting strip containing sharp 90${}^{\ensuremath{\circ}}$ or 180${}^{\ensuremath{\circ}}$ turns, the zero-field critical current at $H=0$ is reduced because vortices or antivortices are preferentially nucleated at the inner corners of the turns, where current crowding occurs. Using both analytic London-model calculations and time-dependent Ginzburg-Landau simulations, we predict that in such asymmetric strips the resulting critical current can be increased by applying a perpendicular magnetic field that induces a current-density contribution opposing the applied current density at the inner corners. This effect should apply to all turns that bend in the same direction.