Angular dependences of the critical field of superconducting superlattices. Experiment

The orientation dependences of the critical magnetic fields Hc(Θ) of V/Si superconducting superlattices with various thickness of the vanadium layers and silicon layers with s=30 A are investigated. For a study of the angular dependences of Hc, samples are chosen in which crossover from a threedimensional behaviour near the transition temperature to two-dimensional behaviour at low temperatures occurs at parallel orientation of H and the superlattice layers. It is demonstrated that the crossover phenomenon also affects significantly the orientation dependences of Hc. At low temperatures the Hc(Θ) dependences can be described satisfactorily by the modified Tinkham formula in which the transition to the two-dimensional behaviour is taken into account. The investigation of derivative β=dHc/dΘ|Θ=Θ near parallel orientation is carried out in a broad range of field strength. Good agreement between the experimental dependences of β(H) and the theory for regular superlattices with Josephson links between finite thickness superconducting layers is observed in fields whose strength exceeds the crossover field strength. The deviation from the theoretical dependence of β(H) observed in weak fields can be attributed to superlattice inhomogeneities