Torque magnetization measurements on HgBa2CuO4+δ microcrystals withdifferent oxygen doping δ were performed in order to extract the dopingdependence of the effective mass anisotropyγ=√m * c/m * ab, of the in-plane penetration depth λ ab , and of the in-plane coherencelength ξ ab . The anisotropy γ increases monotonically withdecreasing δ, suggesting a smooth 3D–2D crossover in the superconductingproperties on reducing the oxygen content. Within the framework of abipolaronic model this increase can be explained by an increase of thepolaron binding energy with reduced doping.
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