Strong thermal fluctuations in cuprate superconductors in magnetic fields above T_c

摘要

Recent measurements of fluctuation diamagnetism in high-temperature superconductors show distinct features above and below T_c, which can not be explained by simple Gaussian fluctuation theory. Self-consistent calculation of magnetization in layered high-temperature superconductors, based on the Ginzburg-Landau-Lawrence-Doniach model and including all Landau levels is presented. The results agree well with the experimental data in a wide region around T_c, including both the vortex liquid below T_c and the normal state above T_c. The Gaussian fluctuation theory significantly overestimates the diamagnetism for strong fluctuations. It is demonstrated that the intersection point of magnetization curves appears in the region where the lowest Landau level contribution dominates and magnetization just below T_c is nonmonotonic. Our calculation supports the phase disordering picture of fluctuations above T_c.