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

Abstract

Isothermal magnetization curves above the transition temperature Tc 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 in finite fields. The experimental findings are related to phase fluctuations of order parameter in “droplets” having local Tcloc 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.