On the character of the fluctuating diamagnetism above the superconducting transition in La1.9Sr0.1CuO4

Isothermal magnetization curves above the transition temperature T-c in a single crystal of superconducting underdoped cuprate La1.9Sr0.1CuO4 are reported. In the low-field range, H <= 1 kOe, and for T within Tc + 2 K, evidence is given of a fluctuating diamagnetism different from the one expected from the Ginzburg-Landau theory infinite fields. The experimental findings are related to phase fluctuations of order parameter in "droplets" having local Tc(loc) higher than the bulk resistive Tc, a general phenomenon in cuprates and intrinsic consequence of charge inhomogeneities at mesoscopic level. The temperature dependence of the droplets size suggests a percolative character of the transition.