Evidence for Fluctuation Effects above $T_c$ in Isotopically and Metallurgically Pure Bulk Type-I Superconductors

Magnetic measurements of superconducting transitions of very pure isotopically separated bulk samples of Ga and Zn reveal a large "paraconductive" effect. This is contrary to the prediction for such systems by Aslamazov and Larkin based on corrections to first order in the fluctuations in the system. It is suggested that this discrepancy may be explained by increased electron pair lifetimes due to the absence of isotopic and other scattering of phonons allowing higher order processes to be significant.