DOPING DEPENDENCE OF SUPERCONDUCTING PARAMETERS IN HGBA2CUO4-CRYSTALS(DELTA SINGLE)

Magnetization measurements on HgBa2CuO4+delta microcrystals with diffe rent oxygen doping delta were performed using a miniaturized torque se nsor. 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 len gth xi(ab) was extracted. The anisotropy gamma increases monotonically with decreasing delta, suggesting a smooth 3D-2D cross-over in the su perconducting 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 explai ned by an increase of the polaron binding energy with reduced doping. (C) 1998 Elsevier Science B.V.