Anomalous behavior of phonons in superconducting ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ detected by far-infrared spectroscopy

We report anomalous behavior of phonons in superconducting ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10}$ at ${\mathit{T}}_{\mathit{c}}$(∼112 K) detected by a far-infrared reflectivity study of a ceramic sample. Our results indicate strong and abrupt softening of an infrared-active phonon and a decrease of oscillator strength of this and of another phonon. We associate the effects with anomalous vibrations of the bridging oxygen in the BaO layers and the off-center oxygen in the TlO layers, respectively. Our results give experimental evidence for strong electron-phonon interaction.