Some studies of the superconducting transition in purified tantalum

Extremely sharp magnetic transitions from the superconducting to the normal state are found for highly purified tantalum specimens with residual resistivities approaching 1×10-3 μ ohm cm. Negligible flux trapping and pronounced supercooling is found to occur in these samples near the transition temperature Tc. Values of Tc as high as 4.483A°K±.002A°K and of the critical field at 0A°K, H0, as low as 830±8 gauss were found for these specimens. The critical field curve is found to have a maximum deviation from a parabolic temperature dependence of about 3%. For tantalum the transition temperature decreases with increasing residual resistivity in much the same way as that observed by Serin and co-workers in dilute substitutional alloys. Some investigation is made of the current dependence of the resistance transition in a magnetic field. © 1960 The American Physical Society.