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Diamagnetism of YBa2Cu3O6+x crystals above Tc : evidence for Gaussian fluctuations

The magnetization of three high-quality single crystals of YBa2Cu3O6+x, from slightly overdoped to heavily underdoped, has been measured using torque magnetometry. Striking effects in the angular dependence of the torque for the two underdoped crystals, a few degrees above the superconducting transition temperature (Tc) are described well by the theory of Gaussian superconducting fluctuations using a single adjustable parameter. The data at higher temperatures (T) are consistent with a strong cut-off in the fluctuations for T >∼ 1.1Tc. Numerical estimates suggest that inelastic scattering could be responsible for this cut-off.

high temperature superconductors; magnetism; superconducting fluctuations

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