Effect of ${\mathrm{HgI}}_2$ intercalation on ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{y}}$: Interlayer coupling effect

By intercalating large ${\mathrm{HgI}}_2$ molecules between the ${\mathrm{Bi}}_2$ ${\mathrm{O}}_2$ layers in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{y}}$, the distance between the ${\mathrm{CuO}}_2$ blocks was significantly extended up to 7.2 Å. The superconducting properties of this system were measured in various magnetic fields applied perpendicular to the ${\mathrm{CuO}}_2$ planes. This system showed large positional fluctuation of the vortex even far below the transition temperature due to the reduction of dimensionality. The change of the thermodynamic parameters is well explained by the model of Josephson-coupled superconductivity. However, the interlayer coupling strength did not change the transition temperature drastically, which does not support the suggestion of Wheatley, Hsu, and Anderson of coherent hopping of the valence bond pair between the ${\mathrm{CuO}}_2$ layers. © 1996 The American Physical Society.