Relaxation Time of the Cooper-Pair Density in Tin

The relaxation time ${\tau }_R$ for the density of superconducting electrons to achieve equilibrium with a change in current density has been measured near $T_c$, using a large, chopped dc and a small continuous rf current. The changeover from $\omega {\tau }_R\ll 1$ to $\omega {\tau }_R\gg 1$ has been observed in the frequency range $30 \mathrm{MHz}<~f<~900 \mathrm{MHz}$. In the temperature range $0.95<~\frac{T}{T_c}<~0.995$, the relaxation time was found to be ${\tau }_R=2.6\mathrm{}\times {10}^{-10\mathrm{}}{(1-\frac{T}{T_c})}^{-\frac{1}{2}}$ sec.