Interpretation of Lorentz microscopy observations of vortices in high-temperature superconductors with columnar defects

In order to interpret recent experimental observations of superconducting vortices interacting with tilted columnar defects in high-temperature superconducting materials, we have extended to the case of anisotropic materials our Fourier space approach for the calculation of the electron optical phase shift experienced by the high-energy electrons in a transmission electron microscope. The case of a London vortex having its core not perpendicular to the specimen surfaces is considered. The same configuration is also analyzed in the framework of a simplified pancake model and the influence of the number of stacks on the phase shift and images is investigated. The results obtained by the two models are compared between them and with the experimental results. The agreement between theory and experiment confirms that anisotropy plays a major role in affecting the electron microscopy images.