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

Abstract Isothermal magnetization curves above the transition temperature T c in a single crystal of superconducting underdoped cuprate La 1.9 Sr 0.1 CuO 4 are reported. In the low-field range, H ⩽1 kOe, and for T within T c +2 K, evidence is given of a fluctuating diamagnetism different from the one expected from the Ginzburg–Landau theory in finite fields. The experimental findings are related to phase fluctuations of order parameter in “droplets” having local T c loc higher than the bulk resistive T c , 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.