Paramagnetic Effect in Superconductors. III. Measurements on Hollow Cylinders of Mercury and Tin

The circular flux which is set up by a longitudinal current passing through a hollow cylinder has been measured in the intermediate state by ballistic and fluxmetric methods. The flux has a maximum in the transition region and drops to zero in the pure superconducting state, which is in qualitative agreement with theoretical predictions. The dependance of the maximum of the flux increase on the current and on the ratio of the inner to the outer diameter of the sample was found to be different from the the theory. It was found, in particular that the ratio ̃ \~K_mφ of the maximum flux, Φₘₐₓ, to the flux in the normal conducting state Φₙ is not independent of the current. It is not possible to correct the theory from these measurements alone. However, it seems very likely that the correction which has to be applied here is intimately connected with the correction term 1-IgI which has to be applied to the theory of the paramagnetic effect.It was further found that the value of the maximum of the circular flux does not change if a longitudinal magnetic field is superimposed. This is in line with theoretical predictions. The longitudinal field intensity in the hole and the resistance of the sample were also measured and the results compared with the present theory. The technique of introducing currents up to 15 amp into the cryostat and an all-metal Dewar vessel are described.