Effective medium theory for superconducting layers: A systematic analysis including space correlation effects

We investigate the effects of mesoscopic inhomogeneities on the metal-superconductor transition occurring in several two-dimensional electron systems. Specifically, as a model of systems with mesoscopic inhomogeneities, we consider a random-resistor network, which we solve both with an exact numerical approach and by the effective medium theory. We find that the width of the transition in these two-dimensional superconductors is mainly ruled by disorder rather than by fluctuations. We also find that tail features in resistivity curves of interfaces between LaAlO3 or LaTiO3 and SrTiO3 can arise from a bimodal distribution of mesoscopic local T-c's and/or substantial space correlations between the mesoscopic domains.