Superconducting properties of indium in the restricted geometry of porous Vycor glass

The superconducting transition of indium in 56-{}-pore Vycor glass has been studied through resistance and magnetic-susceptibility measurements. The confined indium behaves like a ``dirty'' type-II superconductor, and the superconducting transition consists of ItwoR transitions, which become well separated in applied magnetic fields. While the lower critical field Hcˡ follows de Gennes's prediction of Hc2(T), the higher critical field Hcᵘ has an unusual dependence of (1-T/Tc{)}1/2$. The possible origin of this transition is discussed in terms of the microstructure of the composite.