Quantum Phase Transitions and Superconductivity in Single- and Two-Layer Cuprates in the Multiband Theory of Hubbard Fermions

We consider the doping dependence of the normal and superconducting properties of La 2 Sr 2− x CuO 2 and YBa 2 Cu 3 O 7 in the low energy effective model based on the ab initio LDA+GTB calculations. With doping we have found a concentration region with electronic instability of the uniform state. We have shown that two quantum phase transitions (QPT) of the Lifshitz type correspond well to the experimental phase diagram. For superconducting state we have considered both magnetic and phonon mechanisms of pairing.