Imaging flux distributions around superconductors: Geometrical susceptibility in the Meissner state

Experiment and analytical calculations show that the demagnetizing field of a superconductor is a sensitive probe of quantities otherwise difficult to measure, such as the sample-probe distance in flux-density imaging experiments and the field of first flux penetration H_p. In particular, the ratio of the maximum field measured above the superconductor edge and the applied field can be determined unambiguously so as to define a linear "geometric" susceptibility. The evolution of this susceptibility with field depends on the regime of flux penetration and can be used as a means to determine H_p and the effect of a parallel field component in magneto-optical imaging experiments.