Doping dependence of superconducting parameters in HgBa2CuO4+δ single crystals

Magnetization measurements on HgBa2CuO4+delta microcrystals with different oxygen doping delta were performed using a miniaturized torque sensor. From angular dependent torque measurements the doping dependence of the effective mass anisotropy gamma = root m(c)*/m(ab)*, of the in-plane penetration depth lambda(ab), and of the in-plane coherence length xi(ab) was extracted. The anisotropy gamma increases monotonically with decreasing delta, suggesting a smooth 3D-2D cross-over in the superconducting properties on reducing the oxygen content. The increase of gamma may be due to an increase of the effective mass of the charge carriers, which in the framework of a bipolaronic model can be explained by an increase of the polaron binding energy with reduced doping. (C) 1998 Elsevier Science B.V.