Model of superconducting vortices in layered materials for the interpretation of transmission electron microscopy images

More realistic simulations of the magnetic field and electron optical phase shift associated to pancake vortices in layered high-T-c superconducting specimen require a number of layers larger than 7, the practical upper limit set by the discrete algebraic approach followed so far. This goal can be achieved by resorting to a continuum approximation of the screening layers above and below the one containing the pancake vortex. It is thus possible to increase the number of layers and to investigate more exotic vortex core structures than those represented by the pancakes pinned at tilted columnar defects. In particular it will be shown how recently observed dumbbell-like contrast features in the out-of-focus images of superconducting vortices forming a large angle with the specimen surfaces can be interpreted as due to a kinked structure of the pancakes.