Phonon echo in high-temperature superconductors as a nonlinear magnetoacoustic phenomenon

The nonlinear behavior of a phonon echo signal in high-temperature superconductors is studied experimentally. It is demonstrated that conventional consideration of anharmonic effects is insufficient for comprehensive explanation of the echo signal behavior. It is shown that the nonlinear properties of the phonon echo should be taken into account when the phonon echo is used as a means for studying superconductor parameters. An increase in the elastic nonlinearity in iron-doped yttrium ceramics is found.