Double-step resistive superconducting transitions of indium and gallium in porous glass

We studied indium and gallium in porous glass by resistance and magnetization measurements. For indium in porous glass, a very sharp superconducting transition is observed at T₁=4.0±0.05K. When a 1.5 T magnetic field is applied, there is a second transition at T₂~3.5K. At 3.5 K, the field dependence of resistance $R(H)$ indicates two transitions at Hcᵘ~1.4 and Hcˡ~0.4T separated by a plateau. For indium in porous glass, the origins of two-step transitions in $R(T)$ and $R(H)$ might be the same. At Hcᵘ (or T₁) the individual grains of indium in porous glass become superconductors and at Hcˡ (or T₂) all grains are coupled. For gallium in porous glass, two superconducting transitions of $R(T)$ at T₁=7.0 and T₂=6.3K are observed. Between 6.35 and 6.30 K, $R(T)$ increases sharply with decreasing temperature. The quasiparticle tunneling or the conductor-superconductor-conductor coupling might cause the sharp rise in resistance between 6.35 and 6.30 K. At 6 K, there are two transitions at Hcᵘ=2.1T and Hcˡ=1.1T in the $R(H)$ for gallium in porous glass. The two different transitions of $R(H)$ might be caused by a filamentary ``internal structure'' of gallium crystallites. There is no diamagnetism at T₁. The magnetic transition temperature TM at 3, 4, 5, 6, and 7 T are measured; for all the cases, TM<T₂.