Pairing and Coherence Transition in La1.82Sr0.18CuO4 Strongly Two-Dimensional Superconductor

We report conductivity fluctuation measurements in the La1.82Sr0.18CuO4 high temperature superconducting material. The conductivity fluctuation analysis was performed by utilizing the concept of the logarithmic derivative of the conductivity excess. Close and above the critical temperature Tc, we experimentally determine the occurrence of Gaussian and critical fluctuation regimes. Systematic measurements of conductivity as a function of temperature were performed for several values of transport current j. Fluctuation analysis close to the zero resistivity temperature Tc0 was performed and we clearly identified a characteristic exponent, which is analyzed by the dynamical scaling theory and considering a percolation-like transition in a frustrated and disordered system. The observation of a glass-like behavior in our experiments permits to interpret our results as corresponding to a vortex-glass regime.