The spin-bag approach to the high-temperature superconductivity is presented in detail. The general argument that the local supression of the electronic pseudogap leads to an attractive interaction of the quasiparticles is substantiated by the detailed calculation of the pairing potential mediated by the collective modes of the spin-density-wave background. In particular, the spin-wave spectrum, the sublattice magnetization, and the spectral distribution of the collective modes are studied within the random-phase approximation. In the low-doping limit, different shapes of the Fermi surface give rise to a superconducting gap which formally has $d$-wave- or $p$-wave-like symmetry, however the gap has no nodes on the Fermi surface. Therefore, the superconducting properties of our model are analogous to those of a conventional $s$-wave (i.e., nodeless) BCS superconductor. We also discuss possible bag effects in the large-$U$ Hubbard model and in charge-density-wave systems. Finally, the relation of our work with other approaches and with experiment are discussed briefly.

• Received 16 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.11663