  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.
