Raman scattering investigation of superconducting Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O

TL;DR

This study uses polarized Raman scattering to analyze phonon modes in the superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O, revealing insights into its lattice dynamics and possible electronic interactions near 125 K.

Contribution

First-principles comparison of Raman-active phonon modes in Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O and identification of a temperature-dependent anomaly related to electronic interactions.

Findings

Seven Raman modes observed, matching calculations.

Weak electron-phonon and spin-phonon coupling indicated.

Anomaly at 125 K suggests electronic interactions in Ti$_2$O planes.

Abstract

We have performed polarized Raman scattering measurements on the newly discovered superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O$_{2}$ ($T_c = 21$ K). We observe seven out of eight Raman active modes, with frequencies in good accordance with first-principle calculations. The phonon spectra suggest neither strong electron-phonon nor spin-phonon coupling and vary only slightly with temperature, except for one E$_g$ mode associated with large displacements of As atoms near the Ti$_2$O planes. We also identify a small anomaly around 125 K in the linewidth of a A$_{1g}$ mode involving the same As atoms. Our results suggest that the transition at 125 K is most likely driven by electronic interactions taking place in the Ti$_2$O planes.