ABSTRACT
The conductor’s current moves within the weakly coupled layer of copper II ions (Cu2+), avoiding the presence of the oxygen ions. At room temperature, and with no doping,* cuprates are antiferromagnetic† insulators. Every atom of copper II has one unpaired spin. The outer electron conguration for the ground state dication, Cu2+, is 3d9. In these structures, the unpaired electrons on the copper ions are antiferromagnetically‡ coupled in the crystal, so a conduction band cannot be formed. Introduction of small amounts of unpaired electron dopants into the matrix produces lattice defects in the structure and provides a route for uncoupling the antiferromagnetism. The effect of antiferromagnetism on the ability of a system to form a conduction band is crystal-axis dependent. The conductivity effect is also dependent on the spatial orientation of the atoms that are conducting, and those that are antiferromagnetically coupled. It is not possible for an atom to be both antiferromagnetically coupled, and a conductor in the same geometric coordinate. From this starting point, addition of a proper dopant to the matrix can convert the insulating material to a superconductor that has a critical temperature higher than the boiling point of liquid nitrogen, Tc > 77 K.
