A two-band model for the phase separation induced by the chemical mismatch pressure in different cuprate superconductors

A two-band model is used to study the phase separation in systems with different kinds of strongly correlated charge carrier, with a special emphasis on cuprate superconductors near optimum doping. We show that such a system can decompose into two metallic-like phases with more and less localized carriers. This phase separation is controlled by the energy splitting between the two bands. In cuprate superconductors, this energy splitting can be related to the internal chemical pressure on the CuO2 layer due to interlayer mismatch. The interplay between the surface energy of nanoscale inhomogeneities and the long-range Coulomb interaction determines the geometry of the phase-separated state (dropletor stripe-like, depending on doping). The model is able to reproduce the regime of phase separation at doping higher than 1/8 in the experimental pressure–doping–Tc phase diagram of cuprates at large microstrain as it appears in superoxygenated La2CuO4. (Some figures in this article are in colour only in the electronic version)