Two-dimensional fluctuations in the magnetization of the high-temperature superconductor LaBaCaCu 3O 7− δ

Abstract

We report measurements of magnetization and diamagnetic susceptibility in polycrystalline LaBaCaCu3O 7− δ in high magnetic fields (20–50 kOe). The sample has a zero-field transition temperature T c0 =77 K and a transition width of 2.0 K. The results show large fluctuation effects, which can be explained by Ginzburg–Landau fluctuation theory for a two-dimensional system. Using a theoretical model based on the lowest Landau-levels approximation, the magnetization data are fitted with good agreement. The weak-field fluctuation diamagnetic susceptibility above T c can be fitted well in terms of the 2D Lawrence–Doniach model.