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<sub>x2–y2</sub> 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<sub>2</sub> plane; one hole-pair covering 9 - 10 two dimensional CuO<sub>2</sub> unit cells in 3d<sub>x2–y2</sub> configuration. In the investigation of c-axis hole-pairs, cuprate superconductors have been sub-divided into three categories depending on the number of CuO<sub>2</sub> 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<sub>2</sub> planes, the order parameter is of 3d<sub>z2–x2</sub> type in zx-plane with lobes along both the axes much constrained. For cuprates with a single CuO<sub>2</sub> layer, the order parameter is of 3d<sub>x2–y2</sub> type, but its dimensions are less than a-, b-lattice constants

Hole-Pair Formation in Cuprate Superconductors despite Antiferromagnetic Fluctuations

“…We have proposed models of preformed hole-pairs in cuprates [3]- [5] on the basis of FM spin fluctuation in (CuO) 4 plaquette of CuO 2 plane, but there is plethora of evidence that AFM fluctuations are intrinsic properties of cuprates. We will now show that hole-pairs can be formed on the same lines as done earlier without consideration of AFM fluctuations.…”

“…We have proposed models of preformed hole-pairs [3]- [5] for resistanceless current flow in the a-b plane and along c-axis of cuprate superconductors. For better understanding of this paper, it should be read in conjunction with the paper in Ref.…”