The softening of the IR active 300 cm−1 phonon mode in Tl-2223 superconductor, aroundTc has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane, and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon interaction atTc has been emphasized.
Volume 94, 2020
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