Superconducting Transition Temperature of High-Purity Tantalum Metal

The superconducting transition temperature of a high-purity sample of tantalum has been measured and a zero-field value of 4.457^∘{}K±{}0.003^∘{}K obtained. The ratio of room temperature resistivity ρ₂₉₅ to the residual resistivity ρ4.2 gave a measure of the purity of the sample, a value of 250 being obtained. These results compare very well with those of Budnick. The value of (dHcdT) near the zero-field transition temperature was -358 oersteds/^∘{}K. An approximate theoretical estimate similar to that done by Pippard for tin shows that small amounts of impurity as measured by the residual resistance ratio will give a decrease in transition temperature of about half that observed experimentally.