Crossover from superconductivity fluctuation to vortex picture in the vortex state of high-Tc cuprate superconductors

In this paper, we introduce our recent results on superconductivity fluctuation measurement of high-T-c cuprate under finite magnetic field both for the hole-doped La2-xSrxCuO4 (LSCO) and the electron-doped La2-xCexCuO4 (LCCO). Under finite magnetic fields, the scaling relation was valid only for weak fields, and for higher fields, aspects as vortices appeared. However, even at low temperatures, just above the first-order phase transition of the vortex lattice, vortex picture alone cannot describe the data satisfactory. Thus, we need a unified theory for the description of a large superconductivity fluctuation under finite magnetic fields for high-T-c cuprates.