Spin degrees of freedom and flattening of the spectra of single-particle excitations in strongly correlated Fermi systems

The impact of long-range spin-spin correlations on the structure of a flat portion in single-particle spectra xi(p), which emerges beyond the point where the Landau state loses its stability, is studied. We supplement the well-known Nozieres model of a Fermi system with limited scalar long-range forces by a similar long-range spin-dependent term and calculate the spectra versus its strength g. It is found that Nozieres' results hold as long as g > 0. However, with g changing its sign, the spontaneous magnetization is shown to arise at any nonzero g. The increase in the strength \g\ is demonstrated to result in shrinkage of the domain in momentum space, occupied by the flat portion of xi(p), and, eventually, in its vanishing. (C) 2003 MAIK "Nauka/Interperiodica".