Intermediate-state structures of type-I superconductors

We have investigated pattern formation in the intermediate state of type-I superconductors, and have carried out accurate measurements of the dominant spatial periods of the patterns formed, including those related to a widely observed corrugated state. The relationship between the dominant spatial frequency and applied field is compared with the old theory of Landau from 1937 as well as to a recent theory proposed by Goldstein, Jackson, and Dorsey [Phys. Rev. Lett. 76, 3818 (1996)] in which the Meissner state is replaced by current loops. The agreement with the latter model is significantly better than with earlier ones. We propose an alternative interpretation for the current-loop theory based on the representation of the field by Fourier series, which also gives us an understanding of the stability of small amplitude corrugations.