Crossing fields in thin films of isotropic superconductors

We study interactions of perpendicular and longitudinal magnetic fields in niobium films of different thickness in a wide range of temperatures below the superconducting transition temperature (T C). In 100-nm Nb film at all temperatures the longitudinal field H || practically does not influence the dynamics of the normal flux. However, in 200-nm Nb film, a considerable anisotropy in the vortex motion is found with advanced propagation of the normal flux along H || at T > T C /2 and the preferential jumpwise growth of the thermomagnetic flux dendrites across H || at T < T C. Appearance of the in-plane vortices and their cutting reconnection with tilted vortices induced by the normal field H ⊥ is the reason for the observed anisotropy in the thicker film. Absence of the in-plane vortices and much smaller tilt of vortices generated by H ⊥ explain the isotropic normal flux dynamics in the thinner film. Our results open an alternative way of manipulating both slow vortex motion and fast thermomagnetic avalanches.