А contribution to the theory of exchange amplification in high-temperature superconducting systems

The effect of exchange amplification of electron-phonon interaction in hightemperature superconducting systems has been considered and the upper bound of applicabllity of quasi-linear equations has been determined. It has been show11 that these equations are valid if the resonance value of tl1e wave vector $k_r=max(k_{r_{1}},k_{r_{2}})\ll p_F/\hbar$, where PF is tl1e Fermi momentum, as $k_r\sim k_c$, то $\hbar k_c/p_F$. It follows that the quasi-linear theory of high-temperature systems can Ье used to calculate the critical temperature $Т_с$ when the spin-phonon coupling parameter ($\zeta\gg 1$, and to determine the criteria for synthesizing new high-temperature superconducting materials.