Superconductivity of four-layer HgBa 2Ca 3Cu 4O 10+ δ

Abstract

The magnetization of the four-layer superconductor HgBa 2Ca 3Cu 4O 10+ δ with T c≃125 K is presented. The high-field magnetization around T c( H) follows the exact two-dimensional scaling function given by Tešanović and Andreev. This feature is contrary to the inference that the interlayer coupling becomes strong if the number of CuO 2 planes in a unit cell increases. Also, the fluctuation-induced susceptibility in the low-field region was analyzed by using the modified Lawrence–Doniach model. These analyses lead us to conclusion that two among the four CuO 2 layers are in states far from their optimal doping levels.