Introduction

Abstract

Following the discovery of the disappearance of electrical resistance in a “superconducting” material at low temperatures by Kamerlingh Onnes in 1911, a perhaps more fundamental aspect of superconductivity has been uncovered by MEISSNER and OCHSENFELD in 1933, when they observed that a superconductor, placed in a weak magnetic field, completeley expels the field from the superconducting material except for a thin layer at the surface. This expulsion of a magnetic field is generally referred to as the Meissner effect [1.1], and, at first sight, may appear to be the end of the story on magnetic flux structures in superconductors. However, as has been shown during the subsequent years, in an applied magnetic field superconductors display a rich variety of phenomena. Here, the Meissner effect only represents the beginning rather than the end.