Model of Preformed Hole-Pairs in c-Axis Transport in Cuprate Superconductors

Abstract

Model of hole-pairs in electrical transport along ab plane in cuprate superconductors has already been proposed. It has been found to be in the shape of 3d x2–y2 orbital of an electron in an atom. This time, model of hole-pairs in transport along c-axis in cuprate superconductors is proposed. In ab-plane, hole-pairs are formed along CuO 2 plane; one hole-pair covering 9 - 10 two dimensional CuO 2 unit cells in 3d x2–y2 configuration. In the investigation of c-axis hole-pairs, cuprate superconductors have been sub-divided into three categories depending on the number of CuO 2 planes/formula unit. There is a little different treatment for finding out the order parameter in each category. Coherence lengths along ab-planes are of the order of a few tens of Angstroms, whereas along c-axis, they are less than even their a-, b-lattice constants. In cuprates with 2 or 3 CuO 2 planes, the order parameter is of 3d z2–x2 type in zx-plane with lobes along both the axes much constrained. For cuprates with a single CuO 2 layer, the order parameter is of 3d x2–y2 type, but its dimensions are less than a-, b-lattice constants.