COMPARISON BETWEEN DISCRETE AND SEMI-CONTINUOUS LAYERED MODELS OF SUPERCONDUCTING VORTICES IN HIGH TC MATERIALS FOR TEM OBSERVATIONS.
In order to interpret Transmission Electron Microscopy observations of superconducting vortices in anisotropic or layered materials we have found the analytical solution for the Fourier transform of the electron optical phase shift for the case of a straight vortex piercing the specimen at arbitrary angle. The layered case suffered from the shortcoming that only a limited number of pancakes; up to 7, is allowed by the discrete approach followed. Seven layers, however, are scarcely representative of the real stack of pancake vortices, especially when the core pierces the specimen at large angles with respect to the specimen normal. In fact, in these conditions, the pancake discrete structure may no longer be buried in the diffraction fringes of the Fresnel image. Moreover, a small number of layers is a limiting factor when more exotic vortex structures with no straight cores are investigated. This drawback has been overcome by a semi-continuous approach, where each pancake layer is considered singularly, and the discrete structure of the other pancakes is substituted by a superconducting continuous medium that carries supercurrent only parallel to the layers, as proposed by Clem and further developed by Coffey and Phipps. The solution for the vector potential has been found by Fourier methods, connecting the general solutions in the vacuum with those in the superconducting regions. The presence of a vortex in the layer is taken into account by considering the layer as an additional superconducting region of negligible thickness. Once the vector potential is found, the electron optical phase shift can be calculated by integrating the vector potential along a straight trajectory suitably chosen in order to take correctly into account the overall geometry of the experimental set-up, including a tilt of the specimen with respect to the electron beam.
- Research Organization:
- BROOKHAVEN NATIONAL LABORATORY (US)
- Sponsoring Organization:
- DOE/OFFICE OF SCIENCE (US)
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 15009504
- Report Number(s):
- BNL-72268-2004-CP; R&D Project: MA 015 MACA; KC0201010; TRN: US200429%%908
- Resource Relation:
- Conference: MICROSCOPY AND MICROANALYSIS 2004, SAVANNAH, GA (US), 08/01/2004--08/05/2004; Other Information: PBD: 1 Aug 2004
- Country of Publication:
- United States
- Language:
- English
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