Improvements in Crystal Growth and Crystal Homogeneity and Its Impact on Physics

Abstract

With the development of the novel crucible material BaZrO₃ in Geneva a new class of 123 — single crystals has become available, the purity of which reaches now semiconductor grade (> 99.995%). Due to the exceptional purity the experiments are not longer obscured by residual impurities and the influence of different oxygen content and distributions could be studied in detail. This has given way to a set of new findings and basic understanding of the physics of high Tc superconductivity. Examples for the impact of this new crystal generation on physics are the reversible suppression of the so called fishtail effect, which is accompanied with the absence of the Schottky anomaly in low temperature specific heat and the calorimetric observation of the vortex lattice melting. On such samples it is possible to observe the vortex lattice by STM without any surface conditioning and to study the influence of pinning centers such as twin boundaries, micro-structural inhomogeneities of the metallic sub-lattice and oxygen vacancies on pinning of vortices.