IMPROVEMENTS IN CRYSTAL-GROWTH AND CRYSTAL HOMOGENEITY AND ITS IMPACTON PHYSICS

With the development of the novel crucible material BaZrO3 a new class of 123 - single crystals has become available, the purity of which re aches now semiconductor grade (> 99.995%). Due to the high purity the experiments are not longer obscured by residual impurities and the inf luence of different oxygen content and distributions could be studied in detail. This has given way to several new findings and to better ba sic understanding of the physics of high Tc superconductors. Examples for the impact of this new crystal generation on physics are the rever sible suppression of the so called fishtail effect, which is accompani ed with the absence of the Schottky anomaly in low temperature specifi c heat and the calorimetric observation of the vortex lattice melting. On such samples it is possible to observe the vortex lattice by STM w ithout any surface conditioning and to study the influence of pinning centers such as twin boundaries and oxygen vacancies on vortices.