The phase transition in superconductors, IV. Aluminium

The interphase surface tension in superconducting aluminium has been measured using techniques previously applied to tin (Faber 1954). It proves to be several times larger than in the latter metal, besides varying rather differently with temperature and showing signs of an interesting dependence on specimen purity. The results are compared with predictions by Pippard (1951, 1953) and Bardeen (1954), and it is shown that the former theory, though less complete, is slightly more successful. On account of its high surface tension aluminium supercools to an unusual extent. In some cases it has been possible to reduce the applied field to 5 % of Hc without nucleation occurring. This behaviour appears to be characteristic of the ideal, flawless metal, and it is explained in terms of a simple model based on the idea of coherence.