A microstructural model of high-Tc superconductivity

A model is given for the spatial distribution of holes in the CuO2 conduction planes of cuprate superconductors. It is suggested that a CuO2 plane consists of regions of two different charge densities. In particular, the CuO2 planes of YBa2Cu3O7 contain nanodomains of a 3 x 3 hole lattice surrounded by interfaces one unit cell wide in which the holes are paired. It is proposed that the hole-pairing mechanism is magnetic exchange coupling and the pairing force is strong, the pairing energy being greater than kT at room temperature. In the superconducting state the existing hale pairs condense and move coherently and collectively around the insulating nanodomains, like trams running around blocks of houses, with one hole on each tramline. The hole pairs move in an elegant manner with hole pairs hopping from oxygen to oxygen via adjacent copper sites. The model explains the superconducting current being in the a-b plane and it also explains the very short coherence lengths. Because the pairing force is very strong the model suggests that room temperature superconductivity might be possible in carefully designed new materials.