Energy Gap ofV3Si

A new technique for measuring energy gaps, based on the proximity effect, was used to study ${\mathrm{V}}_3$Si. A 12 000-Å ${\mathrm{V}}_3$Si film was deposited on sapphire at 1200°C by getter-sputtering followed immediately by the deposition at 300°K of an 80-Å aluminum film. After oxidation of the aluminum, and delineation of the junction area with SiO, a lead film was deposited at 77°K. ${\mathrm{V}}_3$Si induces by proximity effect a gap ($\simeq 2$ mV) in the aluminum film which is in good agreement with McMillan's theory. Furthermore, one can detect the ${\mathrm{V}}_3$Si gap itself as a dip in the relative conductance curve. In the ten samples measured, the value of the ${\mathrm{V}}_3$Si energy gap at 1°K was very close to $\Delta =2.80\mathrm{}$ mV, which correspond to $2\Delta \left(0^{\circ }\mathrm{K}\right)=3.8k{T}_c$. This result confirms the expectation that ${\mathrm{V}}_3$Si is a strong-coupling superconductor. The validity of such a technique is further shown by the fact that the lead phonon peaks are displaced by an energy corresponding to ${\Delta }_{\mathrm{Al}}+{\Delta }_{\mathrm{Pb}}\simeq 3$ mV. Finally, the induced gap in the aluminum remains almost unchanged by a 50-kG magnetic field and disappears only at 17°K (the resistive transition temperature of the ${\mathrm{V}}_3$Si film).