Considerable asymmetry of the critical current in a niobium thin strip of plano-convex section

We experimentally demonstrate that in the presence of an in-plane magnetic field the voltage-current curve of a Nb thin strip having plano-convex cross section exhibits considerable asymmetry of the critical current. The observed behavior can be accounted for by the magnetic field component normal to the top convex surface of the strip. Such a component is inhomogeneous, changes sign in the middle of the strip and affects the three-dimensional vortices that in this system have sections locally perpendicular to the top convex surface, though the magnetic field is applied parallel to the bottom flat surface. These sections play the most significant role in the generation of the observed asymmetry. A maximum asymmetry ratio of about 300% at 4.2K is observed when the strip is in the mixed state and can be ascribed to the balance of the magnetic force due to the inhomogeneous field component and the polarity dependent Lorentz force associated to the transport current.