A two-phase charge-density real-space-pairing model of high-T-c superconductivity

It is usually assumed that high-T-c superconductors have a periodic band st ructure and a periodic charge density, although amorphous low-T-c supercond uctors are known. In this paper, it is suggested that the CuO2 conduction p lanes of cuprate superconductors consist of regions of two different charge densities which do not normally repeat periodically. It is suggested that the pairing of holes occurs in real space in cuprate superconductors. 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 r oom temperature. The bound hole pair is essentially a bipolaron. A real-spa ce model is very tentatively suggested in which the CuO2 planes of YBa2Cu3O 7 contain nanodomains of a 3 x 3 hole lattice surrounded by interfaces one unit cell wide in which the holes are paired. In the superconducting state in this model, the existing hole pairs condense and move coherently and col lectively around the insulating nanodomains, like trams running around bloc ks of houses, with one hole on each tramline. The hole pairs move in an ele gant manner with hole pairs hopping from oxygen to oxygen via adjacent copp er sites. The model explains the superconducting current being in the ab pl ane and it also explains the very short coherence lengths. Because the pair ing force is strong, the model suggests that room-temperature superconducti vity might be possible in carefully designed new oxide materials.