Electron tunnelling evidence for fluxon entry into thin type II superconducting films

摘要: Electron tunnelling from a normal metal into thin type II superconducting films (Pb-In 20 wt%) has been studied as function of magnetic field H and film thickness (600-7000 A) at 4.2 1.5 °K. The behaviour high confirms the work Tomasch: surface superconductivity is quenched Hc2, upper critical field, when perpendicular to surface, but persists Hc3, sheath in parallel (H||). degree conductivity characterized by current profile ΔI, defined tunnel junctions' (I, V) characteristics. For thicker than 1000 A, plot ΔI against H|| exhibits series dips which dependent on temperature. At fields where this structure present, hysteresis found decreasing H. are attributed entry exit fluxons films. Penetration causes fluxon be delayed He0, greater Hc1, Abrikosov lower field. It argued that subsequent will occur mainly close Hen, spacing such permit their hexagonal packing film's finite thickness. Reasonable agreement between calculated values for Hen minima (ΔI, H||) An image calculation barrier escape shows effect becomes less pronounced reduced. thought that, used these experiments, barriers rendered ineffective irregularities so not above He0. In trapped cause H||. A mechanism proposed variation rate produces argument based dubious assumptions microscopic factors governing ΔI.