Critical-Field Curve of Superconducting Lead

The critical field of pure monocrystalline lead has been measured throughout its range. A vibrating phase-boundary technique was used, permitting continuous observation of the boundary between the normal and superconducting phases within the sample. Because of the co-existence of both phases at all times, supercooling and superheating effects are avoided. Departures from thermodynamic equilibrium are small, as is indicated by the very weak hysteresis (as low as several parts in 10 000). The deviation curve is strongly positive, as expected for strong-coupling superconductors. The measured values of the usual superconductive parameters are $T_c=(7.195\mathrm{}\pm 0.006)$ °K, $H_0=803.4\mathrm{}\pm 0.3$ Oe, ${\frac{d{H}_c}{\mathrm{dT}}|}_{T_c}=237.3\mathrm{}\pm 1.1$ Oe/°K.