Superconducting Tunneling in the Low-Temperature Phases of Gallium

The two low-temperature metastable phases of gallium have superconducting energy gap to transition temperature ratios, $\frac{2{\Delta }_0}{k{T}_c}$, of 4.5 for "amorphous" gallium and 3.9 for the crystalline phase, $\beta$-Ga. Beta-gallium shows considerable structure in the tunneling current indicating the presence of several well-defined peaks in the phonon density of states. Structure observed in the "amorphous" gallium tunneling current appears to be a smeared-out version of that observed in $\beta$-Ga.