Upper critical field H-c2 calculations for the high critical temperature superconductors considering inhomogeneities

We perform calculations to obtain the H-c2 curve of high temperature superconductors (HTSCs). We consider explicitly the fact that HTSCs possess intrinsic inhomogeneities by taking into account a nonuniform charge density rho(r). The transition to a coherent superconducting phase at a critical temperature T-c corresponds to a percolation threshold among different superconducting regions, each one characterized by a given T-c(rho(r)). Within this model we calculate the upper critical field H-c2 by means of an average linearized Ginzburg-Landau equation modified to take into account the distribution of local superconducting temperatures T-c[rho(r)]. This approach explains some of the anomalies associated with H-c2 and why several properties like the Meissner and Nernst effects are detected at temperatures much higher than T-c.