Direct Evidence of the Anisotropic Structure of Vortices Interacting with Columnar Defects in High-Temperature Superconductors through the Analysis of Lorentz Images

Abstract

Two types of Fresnel contrasts of superconducting vortices in a Lorentz micrograph, corresponding to pinned and unpinned vortices, were obtained by a newly developed 1 MV field-emission transmission electron microscope on a Bi 2 Sr 2 CaCu 2 O 8þ (Bi-2212) thin specimen containing tilted linear columnar defects introduced by heavy ion irradiation. The main features of the Fresnel contrasts could be consistently interpreted by assuming that the vortices are pinned along the tilted columnar defects and by using a layered or an anisotropic model to calculate the phase shift of the electron wave. The confirmed validity of both models strongly indicates that superconducting vortices in high-critical temperature (high-T c ) layered materials have an anisotropic structure.

A study on the structural–microstructural characterisation and defect structure of Ru based magnetosuperconductor, RuSr2Eu1.6Ce0.4Cu2O10−

“…There are lot of studies on the defect structure of high Tc materials such as Bi based superconductors, yttrium based superconductors and the newly discovered MgB 2 superconductors [1][2][3][4][5], but there are very few studies on the defect structure of Ru based magnetosuperconductors [6].…”

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

“…In particular, the first analysis of the contrast features strongly suggests that anisotropy plays an important role in determining the outcome of transmission electron microscopy experiments. 7,8 Therefore, in order to interpret the experimental results in the most accurate and appropriate way and to properly take into account the influence of anisotropy we have investigated the model of a tilted London vortex in a thin anisotropic slab and, on the other hand, extended the pancake model calculations by increasing the number of layers. The obtained results are presented, discussed, and compared to experimental results taken in a variety of different conditions.…”

Modeling superconducting vortices in high-Tc materials for TEM observations

“…The upper limit of nine layers related to the computer performance has been more than doubled by approximating the screening layers above and below the layer containing a pancake vortex with a superconducting continuum. r Recent transmission electron microscopy (TEM) observations of superconducting vortices interacting with columnar defects in high-T c superconductors have been performed [1]. It was shown that the main features of the out-of-focus contrast could be consistently interpreted by assuming that the vortices are pinned along the tilted columnar defects and by using a layered or anisotropic model to calculate the phase shift of the electron wave.…”

“…Once the solution of the algebraic system for the unknown coefficients of the vector potential in the whole space has been found, the electron optical phase shift is 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 setup, including a tilt of the specimen with respect to the electron beam [1,2]. The field projected in other directions, useful for displaying its main features, is calculated according the same recipe.…”

“…[1] are shown in (b). It should be noted that the total phase difference is only slightly different.…”