Recently experiments on high critical temperature superconductors have shown that the doping levels and the superconducting gap are usually not uniform properties but strongly dependent on their positions inside a given sample. We show here that the large diamagnetic signal above the critical temperature Tc and the unusual temperature dependence of the upper critical field Hc2 with the temperature can be explained taking the inomo-geneities and a distribution of different local critical temperatures into account.

We present a percolation theory for the high-Tc oxides pseudogap and Tc dependence on the hole level. The doping dependent inhomogeneous charge structure is modeled by a distribution which may represent the stripe morphology and yield a spatial distribution of local Tc(r). The temperature onset of spatial dependent superconducting gap is identified with the vanishing of the pseudogap temperature T*. The transition to a superconducting state corresponds to the percolation threshold among regions of different Tc. As a paradigm we use a Hubbard Hamiltonian with a mean field approximation to yield a doping and temperature dependent superconducting d-wave gap. We show here that this new approach reproduces the phase diagram, explains and gives new insights on several experimental features of high-Tc oxides.