Microwave Properties of Superconducting Zinc in the Energy-Gap Frequency Region

Microwave measurements of the relative power absorbed at resonance have been made with a pure, polycrystalline zinc cavity. The data taken in a ${\mathrm{He}}^3$ cryostat covered the frequency range from 50 to 75 kMc/sec and the temperature range from above the superconduting transition, $T_c=0.825\mathrm{}\pm 0.008°$K, down to 0.28°K. The results extrapolated to 0°K yield an energy gap of $(3.01\mathrm{}\pm 0.09) k{T}_c$. The detailed comparison of $\frac{R_s}{R_n}$ versus frequency showed good agreement in the Pippard limit with the BCS calculations scaled to the experimentally determined gap. A plot of $\frac{R_s}{R_n}$ versus $\frac{h\nu }{E_g\mathrm{}\left(0\right)\mathrm{}}$ for zinc and aluminum showed that the law of corresponding states was valid to about 5%.