Model of Strongly Correlated 2D Fermi Liquids Based on Fermion-Condensation Quantum Phase Transition

Abstract

A theory of strongly correlated electron or hole liquids with the fermion condensate is presented and applied to the consideration of quasiparticle excitations in high temperature superconductors, in their superconducting and normal states. This theory describes maximum values of the superconducting gap which can be as big as $\Delta_1\sim 0.1\epsilon_F$, with $\epsilon_F$ being the Fermi level. We show that the critical temperature $2T_c\simeq\Delta_1$. If there exists the pseudogap above $T_c$ then $2T^*\simeq\Delta_1$, and $T^*$ is the temperature at which the pseudogap vanishes. A discontinuity in the specific heat at $T_c$ is calculated. The transition from conventional superconductors to high-$T_c$ ones as a function of the doping level is investigated. The single-particle excitations and their lineshape are also considered. Analyzing experimental data on the high temperature superconductivity in different materials induced by field-effect doping, we show that all these facts can be understood within a theory of the superconductivity based on the fermion condensation quantum phase transition, which can be conceived of as a universal cause of the superconductivity. The main features of room-temperature superconductors are outlined.