Electron spectrum and superconductivity in the t-J model at moderate doping

A microscopical theory of electron spectrum and superconductivity within th e two-dimensional t-J model in paramagnetic state is proposed. By employing the projection technique for the Green functions in terms of the Hubbard o perators self-consistent Eliashberg equations are derived. A strong couplin g of electrons with spin and charge fluctuations due to exchange and kinema tical interactions is obtained. In the normal state, one-electron spectral functions reveal narrow quasiparticle peaks close to the Fermi surface (FS) with an additional broad incoherent band. The FS changes from holelike at low doping to electronlike for hole concentrations delta> 0.3. In the super conducting state we observe d-wave pairing with the maximal T(c)similar or equal to 0.04t at optimal doping delta=0.3. [S0163-1829(99)04513-0].